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ILLINOIS  BIOLOGICAL 
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Vol.  IV  July,  191 7  No.  i 


LIFE   HISTORY  STUDIES   ON 
MONTANA  TREMATODES 


ERNEST  CARROLL  FAUST 


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ILLINOIS  BIOLOGICAL 
MONOGRAPHS 


PUBLISHED  QUARTERLY 

UNDER  THE  AUSPICES  OF  THE  GRADUATE  SCHOOL 

BY  THE  UNIVERSITY  OF  ILLINOIS 


VOLUME  IV 


Urbana,  Illinois 
1918-1919 


s-. 


Editorial  Committee 


Stephen  Alfred  Forbes  William  Trelease 

Henry  Baldwin  Ward 


TABLE  OF  CONTENTS 


VOLUME  IV 

NUMBERS  PAGES 

1     Life  History  Studies  on  Montana  Trematodes.     By  Ernest  Carroll  Faust. 

With  9  plates  and  one  text  figure 1-120 

(Distributed  March  6,  1918) 


2    The  Goldfish  (Carassius  carassius)  as  a  Test  Animal  in  the  Study  of  Toxicity. 

By  Edwin  B.  Powers.     With  graphs  and  tables 121-194 

(Distributed  July  28,  1918) 


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By  Ruth  Higley.    With  3  plates 195-288 

(Distributed  December  31,  1918) 


4    North  American  Pseudophyllidean  Cestodes  from  Fishes.    By  Arthur  Reuben 

Cooper.    With  13  plates 288-5^2 

(Distributed  May  31,  1919) 


ILLINOIS  BIOLOGICAL 
MONOGRAPHS 

Vol.  IV  July,  1917  No.  I 


Editorial  Committee 


Stephen  Alfred  Forbes  William  Trelease 

Henry  Baldwin  Ward 


Published  under  the 

Auspices  of  the  Graduate  School  by 

THE  University  of  Illinois 


Copyright  by  the  University  of  Illinois  1918 
dlstribxtted  march  6,  1918 


LIFE  HISTORY  STUDIES  ON 
MONTANA  TREMATODES 


WITH  9  PLATES  AND 
1  TEXT  FIGURE 


BY 

ERNEST  CARROLL  FAUST 


Contributions  from  the 

Zoological  Laboratory  of  the  University  of  Illinois 

under  the  direction  of  Henry  B.  Ward,  No.  98 


111  III  liiilllMll|lM 

HH  738173 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILMENT  OF    THE    REQUIREMENTS  FOR  THE  DEGREE 

OF  DOCTOR  OF  PHILOSOPHY  IN  ZOOLOGY  IN  THE  GRADUATE 

SCHOOL  OF  THE  UNIVERSITY  OF  ILLINOIS 

1917 


TABLE  OF  CONTENTS 


Pages 

Introduction 7 

Methods  of  Investigation 7 

Biology  of  the  Bitter  Root  Valley 9 

Morphology  of  Trematodes  Foiind 13 

Introduction 13 

Embryology 14 

Parthenitae  (Sporocyst  and  Redia) 18 

Cercaria  General 23 

Integument 27 

Parenchyma 29 

Musculature 30 

Armature 31 

Glands 32 

Excretory  System 36 

Digestive  System 43 

Genital  System 44 

Nervous  System 47 

Description  of  the  Trematodes  Infecting  Mollusks  of  the  Bitter  Root  Valley 57 

Introduction 57 

Monostomata 58 

Cercaria  pellucida  Faust  1917 58 

Cercaria  konadensis  Faust  1917 61 

olostomata 62 

Cercaria  flabelliformis  Faust  1917 62 

Tetracotyle  pipientis  nov.  spec 64 

Cercaria  ptychocheilus  Faust  1917 66 

Distomata 68 

Xiphidiocercariae 68 

Cercaria  crenata  Faust  1917 68 

Cercaria  glandulosa  Faust  1917 69 

Cercaria  diaphana  Faust  1917 71 

Cercaria  dendritica  Faust  1917 72 

Cercaria  micropharynx  Faust  1917 74 

Cercaria  racemosa  Faust  1917 75 

Echinostome  Cercariae 76 

Cercaria  trisolenata  Faxist  1917 76 

Cercaria  biflexa  Faust  1917 78 

Furcocercariae 80 

Cercaria  gracillima  Faust  1917 80 

Cercaria  tuberistoma  Faust  1917 82 

Pathology 84 

Problems  Presented 86 

Interrelation  of  Trematodes 86 

Relation  of  Trematodes  to  Other  Groups 90 

Life  Cycle  of  the  Digenetic  Trematodes 92 

Simamary 94 

Species  Described  in  this  Paper 95 

Bibliography .' 96 

Explanation  of  Plates 1^2 


71  LIFE  HISTORY  OP  TREMATODES— FAUST 


INTRODUCTION 

During  a  two  years'  residence  at  Missoula,  Montana,  from  1914  to  1916 
the  writer  became  acquainted  with  the  biology  of  the  inter-mountain  region 
of  the  Bitter  Root  valley.  The  heavy  trematode  infection  of  the  animals 
in  this  locality  has  led  to  an  investigation  of  the  life  history  of  the  trematodes 
of  the  region. 

An  opportunity  is  taken  at  this  place  to  express  appreciation  to  all  who 
have  aided  in  this  study,  but  especially  to  Professor  Henry  B.  Ward  whose 
kindness  and  sincere  interest  have  made  the  work  possible. 

METHODS   or  INVESTIGATION 

This  study  is  confined  to  the  trematodes  infecting  moUusks.  The  majority 
of  the  collections  were  made  by  Mr.  Norbert  Sager  of  Missoula.  A  sketch 
map  (text-fig.  1)  indicates  the  location  of  each  collection.  The  snails  were 
shipped  in  damp  green  moss  and  arrived  in  excellent  condition. 

These  observations  on  living  material  gave  data  on  the  stages  of  develop- 
ment within  the  mollusk,  on  the  methods  of  locomotion,  on  encystment,  and 
on  the  excretory  system. 

The  worms  were  removed  from  the  infected  tissue  and  placed  in  a  watch 
glass  in  0.3  per  cent  saline  solution.  The  change  from  the  host  tissue  to  the 
sahne  medium  usually  caused  rapid  movement. 

It  is  essential  that  the  excretory  system  be  studied  in  the  living  material 
as,  aside  from  the  vesicle  and  the  main  trunks  of  this  system,  very  little  can 
be  made  out  in  the  preserved  material.  The  delicate  structure  of  the  flame 
cells  and  the  finer  capillaries  makes  it  necessary  that  these  organs  be  examined 
in  living  specimens,  for  in  fixation  they  are  likely  to  "collapse,  even  with  the 
most  careful  technic. 

The  organs  of  the  digestive  system  come  out  equally  well  in  living  and 
preserved  mounts.  Some  systems,  as  a  rule,  can  be  made  out  only  from  pre- 
served and  stained  material.  The  most  important  of  these  is  the  genital  com- 
plex. For  all  ordinary  purposes  the  material  was  fixed  in  Gilson's  reagent, 
altho  equally  good  results  were  obtained  from  a  corrosive-acetic  fixing  agent. 
From  the  preserved  material  toto  mounts  and  sections  were  made,  using  Dela- 
field's  hematoxylin  and  EhrHch's  acid  hematoxyhn  as  stains.  A  strong 
counter-stain  of  eosin  in  the  sections  brought  out  remarkably  well  the  nerve 
fibers  of  the  worms.  Wax  models  were  made  of  the  mature  and  immature 
stages  of  the  nervous  system  of  cercariae  and  parthenitae. 

Care  was  taken  to  keep  the  mounts  acid-free,  and  for  that  purpose  all 
reagents  except  the  destaining  fluid  were  made  slightly  alkaline  with  dessicated 


ILUNOIS  BIOLOGICAL  MONOGRAPHS 


[8 


Text-figure  1.     Sketch  map  of  the  Bitter  Root  Valley,  Montana,  showing 
localities  where  collections  were  made. 


9]  UFE  HISTORY  OF  TREMATODES— FAUST  9 

potassium  acetate.  Some  specimens  were  fixed  without  any  acid  fraction  in 
the  reagent  in  order  to  preserve  the  excretory  granules.  These  granules,  as 
well  as  the  mucoid  cyst  membrane  of  the  encysted  worm,  gave  beautiful 
biuret  and  xanthoproteic  reactions,  suggesting  a  tyrosine  compound. 

BIOLOGY  OF  THE  BITTER  ROOT  VALLEY 

The  snails  commonly  found  in  the  Bitter  Root  valley  are  Physa  gyrina 
Say,  Lymnaea  proxima  Lea.,  and  Planorbis  irivolvis  Say.  They  have  been 
identified  by  Mr.  Bryant  Walker  of  Detroit,  Michigan.  All  of  these  snails 
were  collected  from  the  lower  part  of  the  valley,  but  Planorbis  trivolvis  was 
not  found  in  the  upper  reaches  of  the  river.  These  mollusks  are  the  hosts 
of  the  trematodes  considered  in  this  paper. 

Two  facts  stand  out  predominantly  in  the  study  of  these  parasites:  the 
large  munber  of  species  of  trematodes  in  the  snails  in  the  limited  range  of  the 
valley,  and  the  high  per  cent  of  infection  both  among  individuals  of  a  species 
and  within  the  individual  of  the  species. 

There  have  been  found  in  a  single  season's  collection  thirteen  trematode 
species  in  the  snails  of  the  valley,  and  one  larval  trematode  in  the  squaw-fish, 
Ptychocheilus  oregonensis  Richardson.  A  total  of  fifteen  collections  of  snails 
was  made  during  the  fall  of  1916  and  four  collections  during  May  1917. 
Seventeen  of  these  collections  contained  trematode  infection.  Lymnaea 
proxima  was  taken  eight  times  from  five  different  localities,  Physa  gyrina 
was  taken  eleven  times  from  eight  different  locaHties,  and  Planorbis  trivolvis 
was  taken  three  times  from  two  localities  (Table  I,  see  next  page). 

The  infection  record  shows  that  the  host  is  not  specific.  In  the  infection 
of  mollusks  with  Cercaria  pellucida  the  host  around  Buckhouse  Bridge  was 
Physa,  while  that  up  the  valley  was  Lymnaea.  Cercaria  gracillima  was  found 
both  in  Physa  and  in  Lymnaea  in  the  region  of  Buckhouse  Bridge  from 
different  collections.  Cercaria  trisolenata  was  found  both  in  Physa  and  in 
Lymnaea  in  the  region  of  Buckhouse  Bridge  and  in  the  vicinity  of  Fort 
Missoula.  While  no  parasite  species  was  found  in  more  than  two  of  the  three 
snails  common  in  the  valley,  there  is  reason  to  beUeve  that  the  third  species 
of  snail  might  be  the  host  under  proper  conditions.  This  view  is  contrasted 
with  that  of  Thomas  (1883:106)  who  found  that  only  one  EngHsh  moUusk, 
Lymnaea  trunculata,  "could  serve  as  an  intermediate  host  to  the  liver  fluke," 
altho  this  writer  suggested  that  other  species  of  snails  must  serve  in  other 
countries  as  hosts  to  the  worm.  This  preference  for  a  particular  moUusk  in  a 
particular  locality,  coupled  with  the  abihty  to  select  a  different  molluscan  host 
in  another  locality,  has  been  found  to  hold  true  not  only  for  Fasciola  hepatica, 
but  also  for  Schistosoma  haematobium  (Leiper,  1916)  and  S.  mansoni  (Leiper, 
1916;  Lutz,  1916;  Iturbe  and  Gonzalez,  1917).  When  two  hosts  so  different 
structurally  as  Physa  and  Planorbis  are  equally  heavily  infected,  it  seems 
evident  that  the  stimulus  to  which  the  miracidium  of  the  fluke  responds  can 


10 


ILUNOIS  BIOLOGICAL  MONOGRAPHS 


[10 


TABLE  I 
DISTRIBUTION  OF  CERCARIAE  IN  THE  BITTER  ROOT  VALLEY 


tn 

•^ 

03 

.2 

.52 

rt 

a 

.3 

=^ 

t 

t 

"cS 

at 

1 

•c 

> 

O 

U 

> 

u 

O 

U 

o 
U 

o 
U 

V 

> 

o 
U 

V 

3 

^ 

M 

M^ 

a 

& 

> 

se 

o 

o 

Si 

4) 

il 

tn 

fa 

0) 

1 

d 
o 

c73 

5o 

^ 

3 

.s 

173 

o 

o 

^ 
■^ 

tn 

3 
O 

fi 

c 

tn 

55 

a 

tn 

3 
O 

a 

I 

1 

73 

■1-1 

3 

O 

> 

a 

s 

s 

:^ 

^^^ 

.6 

■u 

a 
o 

rt 

1-1 

O 

ti 

o 

3 

S 

in 

U 

fa 

U 

« 

« 

fa 

u 

<N 

\n 

CO 

fo 

« 

Pi 

fa 

fa 

PQ 

(^ 

SPECIES 

NUMBER  OF  COLLECTION 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

Monostomes 

Cercaria  pellucida 

a 

b 

C.  konadensis 

b 

Holostomes 

C.  flabelliformis 

d 

d 

a 

a 

a 

C.  ptychocheilus 

Distomes 

C.  crenata 

b 

a 

C.  glandulosa 

C.  diaphana 

b 

C.  dendritica 

b 

b 

b 

b 

C.  micropharynx 

C.  racemosa 

a 
c 

a 

a 
c 

b 

b 

b 

C.  trisolenata 

C.  biflexa 

a 

a 

b 

a 
a 

b 

b 

c 
a 

C.  gracillima 

C.  tuberistoma 

a 

a,  Physa  gyriru  b,  Lymnaea  proxima 

Compare  with  map  on  page  8. 


c,  Planorbis  trivolvis        d,  Ptychocheilus  oregonensis 


not  be  specific.  In  the  case  of  Cercaria  trisolenata,  where  the  infection  ranged 
from  22  to  100  per  cent  in  Physa  and  from  50  to  100  per  cent  in  Planorbis, 
the  host  must  be  considered  facultative. 

In  several  instances  the  same  species  of  snail  from  the  same  collection 
harbored  two  or  more  cercariae  (cf.  collections  nos.  3,  6,  7,  13,  16,  17,  18). 
For  example  (Table  I),  at  the  Maclay  Sloughs  both  Cercaria  trisolenata  and 
C.  gracillima  were  found  in  the  same  host  species,  Physa,  in  fact  in  the  same 
individual.  This  case  is  paralleled  by  the  record  of  Cort  (1915:55),  where 
the  sporocysts  of  Cercaria  polyadena  and  C.  refiexae  were  found  within  the  same 
liver  tissue  of  Lymnaea  reflexa.  However,  Ssinitzin  (1911)  in  an  examination 
of  several  thousand  snails  of  six  species,  in  which  he  discovered  twenty-one 
species  of  cercariae,  makes  no  record  of  two  species  in  the  same  host  individual. 

In  the  collection  of  Lymnaea  proxima  from  Buckhouse  Bridge  three  species 
of  trematodes  were  found  as  parasites,  Cercaria  dendritica,  C.  racemosa,  and 


11] 


LIFE  HISTORY  OF  TREMATODES— FAUST 


11 


C.  gracilUma.  In  such  a  case  as  this,  one  species,  C.  dendritica,  was  present 
in  each  host  in  large  numbers,  while  C.  racemosa  was  less  frequent,  and  the 
third  species  of  worm,  C.  gracillima,  constituted  a  very  light  infection  in  only 
one  of  the  thirty-two  snails  examined.  Hausmann  (1897:16)  in  referring  to 
the  dominance  of  one  parasite  species  in  the  individual  host,  regards  this 
phenomenon  as  a  biological  antagonism. 

Turning  to  the  per  cent  of  infection  in  the  snails  collected  in  the  fall  of 
1916  (Table  II),  a  heavy  parasitism  is  found  to  exist.  The  data  are  especially 
significant  when  compared  with  the  records  of  other  investigators.  Cort 
(1915)  gives  detailed  data  for  eleven  species  of  moUusks  collected  from  nine 
localities.  His  collections  were  made  in  the  fall  of  1913.  The  least  per  cent 
of  individuals  infected  was  1.4,  that  for  Pleurocerca  elevatum,  secured  from 
the  Sangamon  River  at  Mahomet,  Illinois.  This  mollusk  contained  Cercaria 
megalura.  The  heaviest  infection  recorded  by  Cort  was  that  with  C.  isocotylea, 
where  an  18  per  cent  infection  was  found  in  Planorhis  trivolvis  from  Urbana, 
Illinois.  The  average  infection  from  Cort's  eleven  species  records  is  8.5  per 
cent.  Ssinitzin  (1911)  has  recorded  data  from  twenty-one  species  of  cercariae 
described  by  him  for  the  vicinity  of  the  Black  Sea  at  Sebastopol.  In  many 
cases  his  records  show  a  uniquely  low  parasitism,  practically  insignificant  from 
a  pathological  point  of  view.    Out  of  1159  individuals  of  Rissoa  venusta  he 

TABLE  II 
INFECTION  RECORD  FOR  CERCARIAE  OF  THE  BITTER  ROOT  VALLEY 


SPECIES 

HOST 

EXAMINED 

INFECTED 

PER  CENT 

1.  Cercaria  pellucida 

a 
b 
b 
a 
a 
a 
d 
b 
a 
b 
b 
b 
b 
b 
a 
c 
a 
a 
c 
a 
a 
a 
a 
a 
b 
a 

18 
16 
16 

34 
10 
12 

6 
22 

5 
16 
14 
29 
32 
29 
12 

1 

8 
18 

2 
71 
12 
18 
29 
71 
32 
19 

1 

5 
5 
5 
3 
3 
6 
3 
2 
5 
5 
3 

18 
3 

12 
1 
2 
4 
1 
5 
1 
1 
5 

33 
1 
1 

5.5 

2.  Cercaria  pellucida 

31.3 

3.  Cercaria  konadensis 

31.3 

4.  Cercaria  flabelliformis 

14.7 

5.  Cercaria  flabelliformis 

30.0 

6.  Cercaria  flabelliformis 

25.0 

7.  Cercaria  ptychocheilus 

100.0 

8.  Cercaria  crenata 

13.6 

9.  Cercaria  glandulosa 

40.0 

10.  Cercaria  diaphana 

31.3 

11.  Cercaria  dendritica 

35.7 

12.  Cercaria  dendritica 

10.3 

13.  Cercaria  micropharynx...- 

56.3 

14.  Cercaria  racemosa 

10.3 

15.  Cercaria  trisolenata 

100.0 

16.  Cercaria  trisolenata 

100.0 

17.  Cercaria  trisolenata 

25.0 

18.  Cercaria  trisolenata 

22.2 

19.  Cercaria  trisolenata 

50.0 

20.  Cercaria  biflexa 

7.0 

21.  Cercaria  gracillima 

8.3 

22.  Cercaria  gracillima 

5.5 

23.  Cercaria  gracillima 

17.3 

24.  Cercaria  gracillima 

46.5 

25.  Cercaria  gracillima 

3.1 

26.  Cercaria  tuberistoma 

5.3 

a,  Physa  gyrina  b,  Lymnaea  prorima       c,  Planorbis  trivoIvU  d,  Ptychocheilm  oregoQenBU 


12  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [12 

found  only  one  was  infected  with  Cercaria  cribrata  and  one  with  C.  metentera, 
or,  in  each  case,  only  a  0.06  per  cent  infection.  The  heaviest  infection  found 
by  Ssinitzin  among  these  twenty-one  species  of  parasites  was  that  of  C.  zernowi 
in  Cardium  exiguutn,  7.0  per  cent.  The  average  for  the  twenty-one  species  is 
only  1.34  per  cent.  In  the  cases  of  the  worms  found  in  Cerithiolum  exile  and 
Rissoa  venusta,  the  percentage  of  infection  is  so  low  that  no  parasites  would 
have  been  found  had  not  a  large  number  of  snails  been  collected  and  examined. 
The  record  of  Iturbe  and  Gonzalez  (1917)  for  the  cercariae  of  Schistosoma 
mansoni  in  Venezuela  shows  a  heavy  infection. 

The  infection  in  moUusks  of  the  Bitter  Root  valley  is  decidedly  heavy, 
altho  it  varies  within  wide  limits  under  different  factors  of  place  and  season. 
The  lowest  percentage  of  infection  found  was  that  with  Cercaria  gracillima  in 
Lymnaea  proxima  at  Buckhouse  Bridge,  3.1.  From  a  different  slough  in  the 
same  locaUty  one  month  later  a  46.5  per  cent  infection  with  this  species  was 
found  in  Physa.  Thus  the  percentage  of  infection  is  found  to  fluctuate  with- 
in a  very  circumscribed  area.  The  least  infection  of  Physa  with  C.  gracillima 
was  from  the  Maclay  Sloughs  farther  down  the  River,  5.5  per  cent.  On  the 
other  hand,  C.  trisolenata  was  found  as  a  hundred  per  cent  infection  in  both 
Physa  and  Planorbis  collected  from  these  same  sloughs.  Taken  as  a  whole 
the  infection  average  during  the  fall  of  1916  for  the  Bitter  Root  moUusks  is 
29.02  per  cent.  The  average  by  host  species  is  somewhat  different,  24.8  per 
cent  for  Lymnaea,  25.16  per  cent  for  Physa,  and  75.0  per  cent  for  Planorbis. 
Leaving  Planorbis  out  of  consideration  because  of  the  few  specimens  collected 
there  is  an  average  infection  of  over  24  per  cent  in  Lymnaea  and  in  Physa. 
The  per  cent  infection  for  May  1917  (not  included  in  table  II)  gives  an  average 
of  11.5  for  Lymnaea,  16.6  for  Physa,  and  50.0  for  Planorbis. 


131  LIFE  HISTORY  OF  T REM ATODES— FAUST     '  13 


MORPHOLOGY  OF  TREMATODES 

INTRODUCTION 

The  progress  in  the  morphological  and  histological  knowledge  of  larval 
trematodes  is  wrapped  up  in  the  development  of  discriminate  observation 
and  interpretation  on  the  part  of  investigators.  This  has  been  aided  in  no 
small  degree  by  the  use  of  better  technic  and  by  better  optical  equipment,  but 
it  is  for  the  most  part  the  observer's  own  expectation  that  differences  must 
exist  in  larvae,  and  his  determination  to  discover  faithfully  and  accurately 
such  a  differentiation  of  structure,  that  has  brought  about  progress  in  this 
line  of  investigation.  No  clearer  conception  of  the  change  in  point  of  view 
can  be  obtained  than  by  a  contrast  of  the  statement  of  La  Valette,  a  worker  in 
the  field  six  decades  ago,  with  the  expression  of  Charles  Sedgwick  Minot  just 
ten  years  ago.  In  his  S3Tnbolae  ad  Trematodum  Evolutionis  Historiam 
La  Valette  (1855:34)  recites:  "nonnullae  Trematodum  larvae  tam  exiguam 
offerunt  differentiam  ut  discrimina  earum  characteristica  vix  commonstari 
queant. "  Minot  (1897 :928)  voices  the  modern  point  of  view  in  his  declaration 
that  "it  is  not  true  that  all  embryos  are  ahke;  on  the  contrary  they  show  class, 
ordinal,  and  generic  differences  from  one  another." 

While  the  writer  fully  agrees  with  the  idea  that  the  most  natural  way  of 
correlating  larval  trematodes  with  the  adult  forms  is  by  a  knowledge  of  their 
Ufe  histories,  yet  such  a  correlation  is  not  always  possible.  Looss  (1896) 
probably  had  the  cercaria  of  Schistosoma  haematobium  among  some  of  the 
furcocercariae  that  came  under  his  observation,  yet  he  was  forced  to  admit 
(p.  167)  that  "tons  ces  efforts  ont  ete,  quant  a  la  Bilharzia  completement 
negatifs, "  The  writer  has  attacked  this  part  of  the  problem  with  the  idea 
in  mind  that  not  only  the  fundaments  of  the  adult  trematode  are  found  in  the 
mature  cercaria,  but  that  even  the  main  descriptive  features  of  the  adult 
trematode  are  already  present,  so  that  the  worker  can  recognize  the  adult 
in  the  larva.  While  it  has  been  impossible  to  show  species  correlations  between 
larva  and  adult  it  has  been  found  in  the  course  of  the  investigation  that  the 
larva  shows  clearly  the  family  features  that  hitherto  have  been  inferred  only 
by  the   "blunderbuss  method"   of  life-history  investigations. 

Probably  none  of  the  adult  trematodes  genetically  related  to  the  larvae 
studied  have  been  described.  Moreover,  the  characters  common  both  to 
larva  and  adult  have  been  overlooked  in  the  study  of  many  adidt  species. 
The  writer  has  been  confronted  with  the  problem  as  to  what  characters  of  the 
larva  are  ephemeral  and  what  ones  are  common  to  cercaria  and  adult  trematode. 
A  thoro  analysis  of  the  groups  studied,  including  Monostomata,  Holostomata, 
and  Distomata,  gives  convincing  proof  that  the  most  constant  systems  in  larva 
and  adult  are  the  nervous,  genital  and  excretory  systems.  Such  systems  and 
organs  as  tail,  cystogenous  glands,  and  stylet  are  distinctly  larval  in  nature 
and  may  or  may  not  show  the  same  relationship  as  the  natural  grouping  based 
on  characters  common  to  both  larva  and  adult. 


14  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [14 

EMBRYOLOGY 

"Larval  trematode"  has  been  used  for  any  phase  of  the  life-history  from  the 
fertilized  egg  to  the  adult  trematode.  This  is  truly  a  wrong  conception  in 
the  hght  of  the  observations  of  investigators  from  early  times  down  to  the 
present.  Workers  have  recognized  sporocyst  and  redia  as  "nurse"  to  the 
progeny.  In  other  words,  they  are  parthenogenetic  individuals.  Ssinitzin 
(1905,  1910,  1911)  has  made  a  wise  separation  of  sporocyst  and  redia  on  the 
one  hand  from  the  cercaria  on  the  other.  He  groups  the  mature  sporocyst 
and  redia  together  under  the  term  parthenita,  or  parthenogenetic  mother. 
This  term  is  used  thruout  this  paper  to  define  the  mature  sporocyst  and  redia 
as  distinguished  from  cercaria  or  other  larval  trematode  of  the  hermaphroditic 
generation. 

The  homology  between  cercaria,  sporocyst  and  redia  in  their  early  stages 
of  development  is  recognized  by  Schwarze  (1886:64),  who  compares  his  studies 
on  the  cercaria's  development  with  those  of  Schauinsland  (1883)  on  miracidia. 
Schwarze  notes  the  similarity  of  the  "cuticula,"  the  sloughing  off  of  the  epider- 
mis, the  location  of  the  solid  entoblast,  which  divides  so  that  a  portion  comes 
to  he  next  to  the  ectoderm  and  another  part  around  the  gut.  He  shows  that 
the  homology  is  very  apparent.  "Die  Keimzellen  des  Embryos  entsprechen 
den  Genitalzellen  der  Cercarie,  die  etwas  abgeplatteten  Epithelzellen  des 
Embryo  den  MeristemzeUen  der  Cercarie."  He  observes  the  similarity  of 
the  excretory  system  in  miracidia,  redia  and  cercaria,  and  adds  "ferner  sind 
sie  ebenfalls  mit  einem  Nervensystem  ausgestattet,  welches  die  grosste  Aehn- 
lichkeit  mit  demjenigen  der  Cercarien  hat." 

Since  the  miracidium,  redia,  and  cercaria  are  not,  in  last  analysis,  three 
parts  of  one  life-history,  but  more  exactly  three  or  more  genetically  related  but 
complete  Hfe-histories,  it  would  not  be  too  much  to  expect,  then,  that  the 
origin  of  germ  layers  in  miracidium,  redia,  and  cercaria  would  be  the  same. 
All  three  generations  arise  by  the  cleavage  and  development  of  a  single  germ 
cell  of  mesodermal  origin.  In  the  miracidium  the  cell  is  always  fertilized; 
in  the  redia  and  cercaria  it  is  always  parthenogenetic.  The  observations  on 
the  similarity  of  origin  of  these  cells  are  extensive,  yet  mostly  isolated,  and 
deserve  re-emphasis. 

The  exact  method  of  development  of  individuals  within  the  sporocyst  or 
redia  has  been  a  matter  of  diversity  of  opinion.  In  general  one  of  two  views, 
budding  or  parthenogenesis,  has  been  supported  by  investigators.  The 
earHer  writers  who  considered  the  origin  of  the  germ  balls  described  them  as 
arising  endogenously.  Thus  Moulinie  (1856:132)  writes:  "les  Cercaires 
naissent,  comme  nous  I'avons  vu  en  parlant  des  Sporocystes,  de  gemmes  plus 
ou  moins  arrondis  qui  se  forment  dans  I'interieur  de  ses  derniers  lorsqu'  ils 
atteint  leur  developpement  normal. "  Then  the  question  arose  whether  or  not 
the  germ  ball  arose  from  the  ordinary  tissues  lining  the  body  cavity  of  sporocyst 
or  redia,  or  v^^hether  special  cells  were  set  apart  as  a  germinal  epithelium. 
Leuckart  (1886:113-125)  asserts  that  in  all  cases  germ  balls  arise  only  from 


151  LIFE  HISTORY  OF  TREMATODES— FAUST  15 

those  cells  which  remain  unquestionably  embryonic.  He  distinquishes  between 
the  condition  in  rediae  and  sporocysts,  for  in  the  former  he  found  a  specialized 
germinal  epitheHum,  while  in  the  latter  all  of  the  cells  of  the  body  wall  remain 
undifferentiated  in  character,  and  in  consequence  are  capable  of  germ  cell 
production. 

Thomas  (1883:119)  found  for  the  sporocyst-redia  generation  of  Fasciola 
hepatica  that  the  germ  balls  which  develop  into  rediae  arise  in  part  from  ger- 
minal cells  already  present  in  the  embryo  (sporocyst),  but  that "  they  gain  an  in- 
crease in  their  numbers  by  the  proHferation  of  cells  lining  the  body  cavity. " 
In  the  rediae  he  asserts  (p.  125)  that  the  majority  of  the  embryos  seem  to  be 
formed  from  the  transformation  of  cells  at  the  posterior  end.  Cells  from  the  body 
wall  become  enlarged,  and  each  of  these  cells  undergoes  segmentation,  giving 
rise  to  a  morula.  Looss  (1892:156,  157)  is  definitely  committed  to  the  view 
that  any  portion  of  the  epitheUum  lining  the  body  cavity  is  capable  of  produc- 
ing germ  balls,  but,  as  a  matter  of  fact,  only  the  posterior  end  (the  vegetative 
end)  performs  such  service.  Later  in  the  same  paper  (p.  167)  he  speaks  of  the 
developmental  stages  as  a  metamorphosis  composed  of  several  generations,  in 
no  sense  comparable  to  parthenogenesis.  Haswell  (1903:500,  501)  describes 
for  the  sporocyst  of  an  echinostome  larva  the  development  of  embryos  from  a 
single  ovarian  mass  at  the  posterior  end  of  the  body. 

Within  more  recent  years  the  problem  of  the  origin  of  germ  balls  has  been 
centered  around  the  criterion  of  the  formation  of  polar  bodies.  Coe  (1896: 
562)  found  no  polar  bodies  in  the  germinal  epitheHum  of  the  sporocyst  and 
redia  of  Fasciola  hepatica.  Because  Reuss  (1903 :470)  found  three  small  gran- 
ular bodies  attached  to  the  germ  balls  of  Distomum  dupUcatum  sporocysts,  he 
concluded  that  maturation  occurred.  Tennent's  work  on  Bucephalus  haimae- 
nus  (1906:649)  supports  the  argument  in  favor  of  the  origin  of  the  germ  cell 
from  the  walls  of  the  body  cavity.  After  the  germ  cell  passes  into  the  body 
cavity  a  "polar  body"  is  cut  off.  Later  Tennent  has  found  that  there  are 
three  cells  in  the  proximity  of  the  germ  cell,  two  of  which  seem  to  be  the  result 
of  division  of  the  first  cell.  Rossbach  (1906:433)  finds  no  cells  which  he  is 
willing  to  call  polar  bodies.  He  concludes  1)  that  the  small  cells  near  the  epithe- 
lium are  not  polar  bodies  because  their  walls  are  not  found  in  direct  continuity 
with  the  germ  cells;  2)  that  the  cells  called  polar  bodies  by  Reuss  are  normally 
present  during  development  of  the  germ  ball,  in  miracidia,  in  sporocysts,  in 
rediae,  and  even  in  the  ovary  of  sexually  mature  trematodes;  3)  that  they  are 
more  abundant  in  the  younger  sporocysts  and  rediae,  and  4)  that  they  are  pre- 
sent in  larger  numbers  than  three's.  Finally  Gary  (1909),  in  his  study  of  the 
germ  cells  of  an  amphistome  sporocyst,  has  found  that  the  germ  balls  arise 
from  cells  of  the  body  wall  which  mature  without  reduction  and  throw  off 
one  polar  body. 

The  contribution  to  the  problem  of  the  meaning  of  the  proHferation  of  germ 
balls  as  described  in  this  paper,  is  based  on  the  development  of  the  germ  ceUs 
in  the  rediae  of  the  holostome,  Cercaria  fldbelliformis  Faust  1917.    In  the 


16  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [16 

anterior  part  of  the  mother  rediae  large  germ  balls  of  both  rediae  and  cercariae 
are  present.  The  germinal  epithelium  is  confined  to  the  posterior  fourth  of 
the  wall  lining  the  body  cavity.  In  some  of  the  larval  rediae  within  the 
mother  rediae  the  earlier  stages  of  the  history  of  the  germ  cells  have  been 
studied.  This  has  enabled  the  writer  to  secure  a  series  of  stages  of  the  germ 
cells  all  the  way  from  the  probable  derivation  of  the  mesoderm  tissue  from 
the  base  of  the  gut  up  thru  maturation  and  segmentation. 

At  a  stage  in  the  development  of  the  redia  when  the  archenteron  is  repre- 
sented by  about  eight  or  ten  large  vesicular  cells  (Fig.  45),  certain  cells  are 
found  wandering  out  from  the  bUnd  end  of  the  gut  and  spreading  thru  the 
body  cavity.  Some  of  these  cells  come  to  he  against  the  wall  of  the  cavity 
and  at  first  appear  as  protrusions  of  the  wall;  later  they  seem  to  constitute  a 
loosely  formed  inner  layer  of  the  wall.  Other  cells  of  this  type  are  found  free 
in  the  body  cavity.  The  majority  of  these  cells  that  have  wandered  out  from 
the  base  of  the  gut  are  oval  in  shape,  and  have  attached  to  them  on  one  side 
a  small,  nodular  protrusion,  consisting  of  the  film  of  cytoplasm  around  a  densely 
granular  nucleus. 

All  of  these  cells,  whether  attached  to  the  body  wall  or  not,  are  to  be  re- 
garded as  germ  cells,  based  on  their  present  structure  and  future  behavior. 
The  small  nodules  are  polar  bodies.  Figure  46  H  shows  this  body  in  process 
of  formation.  The  mitotic  figure  is  in  the  anaphase  stage,  and  was  found  in  a 
germ  cell  free  in  the  body  cavity  of  a  young  daughter  redia.  These  data  on 
the  origin  of  the  germ  cells  from  the  specialized  germinal  mass  at  the  blind 
end  of  the  gut  support  the  thesis  of  Leuckart  (1886:123)  and  Schwarze  (1886: 
48,  49),  that  the  cells  have  preserved  their  original  embryonic  character.  The 
fact  that  the  production  of  the  polar  body  and  consequent  maturation  of  the 
germ  cells  takes  place  in  cells  next  to  the  body  cavity  as  well  as  in  those  free  in 
the  body  cavity,  explains  the  observations  of  Thomas  (1883:115)  that  some 
of  the  cells  from  which  the  germ  balls  are  derived  are  "the  germinal  cells  of 
the  embryo  or  cells  derived  from  them  by  division,  others  are  formed  by  a 
proliferation  of  the  epitheHum  lining  the  cavity  of  the  sporocyst,"  since  these 
two  groups  are  traceable  back  to  a  common  origin  at  the  base  of  the  gut. 

A  description  is  now  given  in  support  of  the  view  that  the  germ  cell  is 
a  true  ovum.  In  its  unmodified  condition  the  germ  cell  is  moderately  incon- 
spicuous, similar  in  all  respects  to  an  undifferentiated  parenchyma  cell.  As  it 
begins  to  change,  the  cell  enlarges,  the  cytoplasm  becomes  granular,  with 
many  interstitial  vacuoles,  and  the  nucleus  comes  to  have  a  clearly  outhned 
membrane  wall.  Frequently  the  chromatin  material  is  massed  into  a  karyo- 
some  (Fig.  46  A).  The  chromatin  mass  now  becomes  oblong  (B)  and  after 
considerable  growth  becomes  coiled  into  a  thick  skein  (C).  The  next  stage 
(P)  shows  the  division  of  the  skein  into  eight  chromosomes.  These  chromo- 
somes arrange  themselves  in  an  equatorial  plate,  and  soon  show  a  longitudinal 
sphtting.  One  of  these  (b)  is  precocious  in  its  behaviour.  It  wanders  toward 
the  edge  of  the  nucleus  and  divides  (6i,  62)  while  the  other  seven  chromosomes 


17]  LIFE  HISTORY  OF  TREMATODES— FAUST  17 

remain  with  their  halves  still  in  contact.  The  precocious  chromosomes  take 
up  positions  toward  the  poles  of  the  cell  (G).  The  other  chromosomes  then 
divide  and  migrate  to  opposite  poles  {H),  one  of  these  daughter  groups  being 
constricted  off  as  a  polar  body  (/).  As  a  result  of  this  process  eight  chromo- 
somes separate  by  longitudinal  splitting,  so  that  half  of  each  goes  into  the  polar 
body  and  half  remains  in  the  cell.  The  polar-body  remains  in  cytoplasmic 
connection  with  the  ovum  while  the  latter  undergoes  another  division.  As  in 
the  previous  division,  simple  mitosis  occurs.  The  chromosomes  ^i,  62  precede 
the  others  in  separation  into  component  halves  {{Fig.  46  /).  In  a  late  anaphase 
of  this  second  division  (/)  the  polar  body  may  divide,  altho  this  is  not  always 
the  case. 

This  second  division  is  not  a  part  of  the  maturation,  for  that  has  been 
accomplished  by  the  expulsion  of  the  single  polar  body:  hence,  it  constitutes 
the  first  division  of  the  mature  ovum.  After  this  {K)  the  polar  body  is  entirely 
separated  from  the  blastomeres  (L)  and  disintegrates.  Thus  maturation 
consists  of  a  single  mitotic  division  with  the  extrusion  of  a  polar  body,  and 
takes  place  without  any  reduction  of  chromosomes.  In  other  words,  the 
process  is  one  of  true  parthenogenesis. 

The  somatic  chromosome  count  of  the  developing  germ  ball  is  eight,  con- 
sisting of  seven  ordinary  chromosomes  and  the  precocious  individual.  In 
support  of  this  statement  is  the  count  of  each  of  the  first  two  blastomeres 
(JfiT,  L),  and  the  chromosome  complex  in  the  late  metaphase  of  an  endoderm 
cell  of  a  morula  {M).  In  the  latter  the  count  is  double,  e.g.,  sixteen,  in  view 
of  the  previous  spHtting  of  the  chromosomes  antecedent  to  separation  into  the 
daughter  chromosome  groups.  The  consistent  tendency  of  the  chromosome 
b  and  its  descendents  to  separate  from  the  chromosome  mass  and  to  divide 
before  the  other  seven  split,  suggests  the  possibility  that  this  chromosome  is  a 
heterosome,  two  of  which  Lindner  (1914)  has  found  in  the  adults  of  Schistosoma 
haematobium. 

In  the  case  of  the  germ  balls  that  never  reach  the  body  wall,  the  process 
of  maturation  takes  place  free  in  the  body  cavity.  For  those  cells  which 
lodge  against  the  wall  and  even  fuse  with  the  wall,  the  process  of  maturation 
and  cleavage  into  two  blastomeres  takes  place  while  the  ovum  is  still  in  con- 
tact with  the  body  wall.  At  this  time  it  is  set  free  and  allowed  to  develop  into 
a  germ  ball. 

In  the  older  mature  rediae  (Fig.  44)  the  epithelial  layer  of  the  body  wall 
Hning  the  body  cavity  consists  of  a  syncytium  in  which  nuclei  are  arranged 
irregularly.  The  cell  boundaries  become  distinct  only  as  maturation  of  the 
cells  approaches. 

Leuckart  (1886:124)  has  stated  that  it  is  relatively  long  after  germ  ball 
formation  before  it  is  evident  whether  the  embryo  is  to  develop  into  a  redia  or 
cercaria.  While  the  chromosomal  history  in  the  rediae  of  Cercariaflabelliformis 
shows  no  difference  between  cells  which  develop  into  daughter  rediae  or  cer- 
cariae,  the  cytoplasmic  history  of  this  species  is  indicative  of  the  generation 


18  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [18 

of  the  offspring  at  an  early  date.  The  cytoplasm  of  the  germ  cells  which 
develop  into  rediae  is  granular  altho  quite  transparent.  It  stains  a  delicate 
lavender  with  Delafield's  hematoxylin.  On  the  other  hand,  from  the  very 
outset  the  cytoplasm  of  the  cercaria  t3^e  of  cell  is  fibrillar,  with  many  large 
intermediate  vacuoles.  It  stains  a  deep  magenta  with  the  same  dye  in  the 
same  section  as  the  rediae  ova.  Figure  46  L  represents  the  first  cleavage  of  the 
cercaria  embryo.  The  chromosome  count  is  identical  to  that  in  each  blastomere 
in  a  redia-forming  embryo.  Subsequent  divisions  are  difficult  to  follow  on 
account  of  the  opacity  of  the  cercaria  germ-balls.  It  is  very  evident,  never- 
theless, that  differentiation  of  layers  and  organs  takes  place  much  more  rapidly 
in  the  cercaria  ovima  than  in  the  redia  ovum. 

The  arguments  produced  by  Rossbach  (1906:433),  to  show  that  there  are 
no  polar  bodies  given  off  by  the  germ  cell,  do  not  hold  in  the  case  of  Cercaria 
flabdliformis.  The  polar  bodies  have  been  found  not  only  in  cytoplasmic 
continuity  with  the  ovum,  but  in  the  actual  state  of  mitosis  preceding  the 
separation  of  the  polar  nucleus  from  the  germ  ball.  Polar  bodies  are  indeed 
more  mmaerous  in  the  young  rediae,  since  this  is  the  period  when  the  majority 
of  the  germ  cells  free  in  the  body  cavity  throw  off  the  polar  body  and  mature. 
Altho  Tennent  has  found  three  bodies  similar  to  those  designated  by  authors 
as  "polar  bodies,"  no  authentic  proof  is  recorded  of  more  than  one  polar 
extrusion  in  the  maturing  germ  cell  of  a  redia  or  sporocyst. 

In  summary,  it  may  be  said  that  the  study  of  the  germ  cells  in  the  rediae 
of  Cercaria  flabelliformis  supports  the  thesis  that  true  parthenogenesis  takes 
place  here;  that  the  germ  cells  are  traceable  to  a  mesodermal  cell  mass  in  the 
region  of  the  bUnd  end  of  the  gut;  that  a  single  polar  body  is  extruded;  and  that 
maturation  takes  place  without  reduction. 

It  is  not  surprising  that  the  details  of  the  germ  layers  have  not  been  worked 
out  in  the  fertilized  trematode  egg,  because  of  the  yolk  inclusions  which  ob- 
scure developmental  stages  and  no  doubt  modify  the  behavior  of  the  segment- 
ing cells.  Yet  it  is  regrettable  that  no  attempt  at  the  precise  origin  of  the 
germinal  layers  has  been  made  on  germ  balls  within  the  sporocyst  or  redia. 
Without  any  effort  at  this  exact  study  of  the  problem  the  writer  has  followed 
in  the  Uving  rediae  of  Cercaria  pellucida  and  C.  konadensis,  and  in  the  sporo- 
cysts  of  C.  dendritica  the  development  of  the  germ  balls  from  the  single  mature 
ova,  thru  unequal  divisions  into  two,  three  and  five  cells,  up  to  the  morula 
stage. 

PARTHENITAE  (SPOROCYST  AND  REDIA) 

Since  the  classic  work  of  Thomas  (1883)  on  the  hfe-history  of  Fasciola 
hepatica,  it  has  been  the  common  custom  to  define  the  sporocyst  and  redia 
in  terms  of  stages  in  the  Hfe-history  of  the  trematode.  The  sporocyst  is  the 
metamorphosed  miracidiimi,  and  the  redia  arises  within  the  sporocyst.  The 
cercaria  is  the  parthenogenetic  offspring  of  the  redia  and  develops  into  the 
adult  trematode.    While  this  represents  a  so-called  typical  life-history,  it  is 


191 


LIFE  HISTORY  OF  TREMATODES— FAUST 


19 


worth  while  to  inquire  into  the  facts  and  see  if  the  outlined  sequence  of  events 
is  always  followed.  In  some  cases  the  sporocyst  is  the  mother  of  the  cercaria, 
in  which  case  the  redia  cycle  has  been  omitted.  The  accompanying  table  (III) 
shows  that  of  the  fifteen  species  treated  in  this  paper  eight  have  cercariae 
derived  directly  from  the  germ  cells  of  the  sporocyst.  Of  the  seven  remaining, 
five  are  known  to  come  from  rediae,  while  the  parthenitae  of  the  other  two 
species  of  larvae  are  not  known. 

TABLE  m 
GERMINAL  EPITHELIUM 


Monostomata 

1.  Cercaria  pellucida 

2.  Cercaria  konadensis 

Holostomata 

3.  Cercaria  flabelliformis.... 

4.  Cercaria  ptychocheilus.... 

5.  Tctracotyle  pipieniis 

Distomata 

Xiphidiocercariae 

6.  Cercaria  crenata 

7.  Cercaria  glandulosa 

8.  Cercaria  diaphana 

9.  Cercaria  dendritica 

10.  Cercaria  micropharynx.. 

11.  Cercaria  racemosa 

Echinostome  cercariae 

12.  Cercaria  trisolenata 

13.  Cercaria  biflexa 

Furcocercariae 

14.  Cercaria  gracillima 

15.  Cercaria  tuberistoma 


PARTHENITA 

SPOROCYST         REDIA 

NON-LOCALIZED 

LOCALIZl 

X 
X 

Z 

rachis 

X 

? 
? 

X 

? 
? 

X 

X 

X 

z 

X 

X 

X 

z 

X 

X 

X 

X 

X 

X 

X 

z 

X 

z 

X 

z 

Types  of  development  are  characteristic  of  certain  groups.  The  Mono- 
stomata, Holostomata,  and  Amphistomata  and  usually  the  echinostome  cer- 
cariae develop  within  rediae.  The  xiphidiocercariae  and  the  furcocercariae 
arise  from  sporocyst  tissue.  A  considerable  modification  of  a  typical  life- 
history,  such  as  is  found  in  Fasciola  hepatica,  is  displayed  among  various  groups 
of  Digenea.  In  1835  von  Siebold  described  a  viviparous  monostome  larva 
under  the  name  of  Monostomum  mutahile,  in  which  the  miracidium  bursts  the 
egg-shell  while  it  is  still  within  the  uterus.  Within  this  miracidiimi,  without 
any  metamorphosis  into  a  sporocyst,  there  develops  a  single  redia.  Schistosoma 
japonicum  has  two  sporocyst  stages,  of  which  the  former  is  covered  with  a 
smooth  and  the  latter  with  a  spinous  integvunent  (Leiper  and  Atkinson, 
1915:202).  This  worm  has  no  redia  stage,  for  the  cercariae  develop  within 
the  secondary  sporocyst.  Cercariae  and  rediae  develop  side  by  side  in  the 
rediae  of  Cercaria  flabelliformis. 

The  sporocyst  is  much  simpler  than  the  redia.  It  is  merely  a  sac  with 
ectoderm  covering,  and  at  times  a  secretory  integimaent.  Occasionally  one 
end  is  partially  muscular.    From  the  inner  waU  of  this  sac  arise  the  germ  balls 


20  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [20 

that  grow  into  the  parthenogenetic  individuals.  In  the  simplest  types  the 
germinal  cell  mass  consists  of  the  entire  internal  layer  lying  next  to  the  ecto- 
derm. Such  a  type  is  seen  in  Cercaria  diaphana  (Fig.  79),  and  in  C.  micro- 
pharynx  (Fig.  94).  In  the  majority  of  cases,  however,  the  germinal  tissue 
is  localized  at  one  end  of  the  sporocyst.  In  two  cases  at  least  there  is  the 
differentiation  of  a  muscular  attachment  organ  at  the  antipodal  end  (C 
dendriiica,  Fig.  87;  C.  racemosa,  Fig.  105).  In  the  furcocercariae,  C.  gracUlima 
and  C.  tuberistoma  (Figs.  147,  157),  there  is  a  rhizoid-like  attachment  at  the 
germinal  end.  In  these  cases  there  seems  to  be  some  evidence  for  regarding 
the  germinal  layer  as  localized  at  the  end  opposite  the  potential  mouth. 

The  redia  is  the  type  of  the  life  cycle  normally  developing  within  the 
sporocyst.  Its  organization  is  much  more  complex  than  that  of  the  sporocyst. 
There  is  a  well-developed  oral  aperture,  a  muscular  pharynx,  and  a  sac-like  gut. 
There  is  a  birth-pore  just  behind  the  collar  region,  on  the  left  side,  sUghtly  ven- 
tral. Two  projections,  usually  in  the  posterior  part  of  the  body,  readily  differ- 
entiate the  redia  externally  from  the  shapeless  sporocyst.  With  some  justifica- 
tion Ssinitzin  (1911:76)  regards  these  projections  as  comparable  to  an  originally 
bifid  tail  of  the  cercaria  as  in  Bucephalus.  In  the  cephahc  region  aroimd  the 
pharynx  there  is  a  nerve  complex  of  highly  differentiated  nerve  cells  and  nerve 
fibers.  These  are  distinguishable  as  a  central  nerve  ring,  with  four  anterior 
and  four  posterior  tnmks.  The  posterior  trunks  do  not  develop  far  caudad. 
The  integimaent  is  well  developed  and  thick,  and  muscular  layers  within  it 
play  an  important  r61e  in  the  movement  of  the  redia,  whereas  the  sporocyst 
depends  almost  entirely  for  its  movement  on  the  motility  of  the  larvae  within 
it.  In  the  mature  redia  the  germ  tissue  is  always  locah'zed  at  the  posterior 
extremity  of  the  body. 

The  development  of  the  germinal  tissue  of  sporocyst  and  redia  has  been 
shown  to  be  the  result  of  the  maturation  of  parthenogenetic  eggs.  The  sig- 
nificant correspondence  between  the  localized  germinal  epithelium  of  the 
parthenita  and  that  of  the  cercaria  may  be  pointed  out  here.  In  most  cercariae 
the  male  germ  cells  are  aggregated  into  a  definite  nimaber  of  testicular  masses, 
in  most  cases,  two.  In  the  apharyngeal  furcocercariae  (the  probable  larvae 
of  the  Schistosomatidae)  the  niunber  of  germ  masses  is  larger.  The  data 
compiled  in  Table  IV,  on  the  better  known  Schistosomatidae,  show  that  the 
nimiber  of  the  testicular  follicles  varies  from  four  to  five  in  Schistosoma  haema- 
tobium, the  mammaUan  parasite  (Looss,  1899:658)  to  about  134  in  Bilharziella 
polonica,  the  avian  parasite.  The  origin  of  these  testes  is  not  described  in 
any  case.  In  all  of  the  adults  the  sexes  are  separate.  In  Cercaria  gracUlima 
(Fig.  149)  the  testicular  masses  are  proliferated  from  a  germinal  mass  at  the 
posterior  extremity  of  the  body,  ventral  to  the  excretory  bladder.  They  are 
nimierous;  some  twenty-four  or  twenty-five  masses  are  foimd  in  this  region  at 
this  stage  of  maturity.  Moreover,  the  female  cell  masses  are  also  present  in 
the  species  at  this  lar\'al  stage,  showing  that  the  animal  is  not  primitively 
unisexual,  but  hermaphroditic.  It  would  be  only  one  step  further  back  in 
the  phylogeny  of  the  group  to  assume  that  the  hermaphroditic  cell  masses  and 


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23]  UPE  HISTORY  OF  TREMATODES— FAUST  23 

the  germinal  epithelium  of  the  parthenitae  arose  from  a  common  type  of  germ 
cell.  In  other  words,  the  germ  cells  of  cercariae  and  parthenitae  are  homolo- 
gous. Stages  in  the  phylogenetic  development  of  the  germinal  epithelium 
may  be  outlined  thus: 

1.  Germinal  epithehum  non-localized.  Example,  Cercaria  diaphana 
(Fig.  79),  C  micropharynx  (Fig.  94).     Sporocyst  cycle. 

2.  Germinal  epithelium  localized;  no  mouth  or  suctorial  apparatus.  Ex- 
ample, C.  glandulosa  (Fig.  67).     Sporocyst  cycle. 

3.  Germinal  epithehmn  localized;  suctorial  disc  or  attachment  organ 
opposite  germinal  cell  mass.  Example,  C.  dendritica  (Fig.  87),  C.  racemosa 
(Fig.  105).    Sporcyst  cycle. 

4.  Germinal  epithehum  localized  opposite  a  true  oral  aperture,  with  phar- 
ynx and  gut  present.     Example,  C  flabelliformis  (Fig.  43).    Redia  cycle. 

5.  Germinal  epithelium  locaHzed  and  specialized  into  two  sorts  of  con- 
jugating  germ   cells,   male   and   female   isogametes.     (Theoretical.) 

6.  Male  germ  cells  prohferated  in  numbers  from  the  mass  of  germinal 
tissue  at  the  posterior  end  of  the  body;  female  germ  cells  more  highly 
differentiated.  Example,  C.  gracillima  (Fig.  149).  Cercaria  stage  of 
hermaphroditic  cycle. 

7.  Germinal  cells  massed  into  a  small  number  of  speciaHzed  glands,  called 
testes  and  ovaries.  Example,  C.  pellucida  (Fig.  18).  Cercaria  stage  of 
hermaphroditic   cycle. 

CERCARIA  (general) 

The  cercaria  is  the  offspring  of  the  parthenita.  It  is  a  highly  specialized 
individual,  homologous  to  the  immature  redia  or  the  sporocyst.  Its  speciaU- 
zation  has  been  accounted  for  by  Ssinitzin  (1910:38-56)  because  of  1)  a  con- 
siderable period  of  free-swimming  hfe,  during  which  it  acquired  a  tail,  and  2) 
a  change  to  parasitism  in  the  vertebrate,  which  was  at  first  facultative,  but 
later  became  obligatory.  There  are  two  types  of  modified  characters  to  be 
accounted  for  in  the  cercaria,  in  addition  to  the  original  characters  common 
to  parthenita  and  cercaria.  The  tail,  the  well-developed  muscle  complex, 
the  nerves  innervating  the  muscle  system,  together  with  the  sahvary  glands 
and  the  sensory  papillae — all  of  these  bear  evidence  of  a  long  period  of  indepen- 
dent life.  When  the  organism  became  parasitic,  first  ectoparasitic,  later 
endoparasitic,  the  highly  developed  muscular  suckers  with  their  nerve  tracts 
were  further  developed,  while  the  stylet  organs  and  cystogenous  glands  were 
differentiated.  The  muscular  specialization  was  of  primary  importance  within 
the  host,  while  the  cyst  served  to  protect  the  worm  during  the  period  of  transfer 
from  larval  to  definitive  host. 

The  cercaria  varies  in  size,  altho  it  is  fairly  constant  for  a  particular  family 
or  genus.  Holostome  larvae  reach  a  size  of  0.63  mm.  in  length  and  0.35  mm. 
in  width  (C.  ptychocheilus).  On  the  other  hand  some  of  the  xiphidiocercariae 
are  much  more  minute,  0. 18  mm.  in  length  by  0.09  mm.in  width.{C. micropharynx). 


24  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [24 

There  are  two  types  of  movement  in  the  cercaria  aside  from  the  apparent 
contraction  and  expansion  of  the  body.  One  of  these  is  concerned  with  the 
forward  movement  of  the  animal  and  depends  on  the  cooperative  action  of 
the  suctorial  organs  and  the  general  bodily  musculature.  The  other  is  caused 
by  the  flagellate  action  of  the  tail.  The  movement  of  the  cercaria  along  a 
forward  path  reminds  one  of  the  rythmic  action  of  a  measuring  worm.  The 
oral  sucker  is  always  used  as  one  organ  of  attachment,  and  the  ventral  or 
caudal  suctorial  disc  supplies  the  other  anchorage.  With  these  two  organs 
of  attachment,  the  larval  worm  applies  the  oral  disc  to  the  object  of  contact, 
while  it  draws  the  posterior  portion  of  the  body  forward  by  the  contraction 
of  all  the  longitudinal  muscles.  This  places  the  posterior  attachment  advan- 
tageously near  the  oral  disc,  so  that  a  relaxing  of  the  longitudinal  muscles 
and  a  synchronous  contraction  of  the  transverse  muscles  throws  the  cephalic 
portion  of  the  worm  far  forward.  In  the  forms  with  well  developed  muscula- 
ture, such  as  monostome  and  echinostome  species,  the  larva  may  appear 
discoid  on  contraction,  while  the  expanded  worm  wiU  assume  a  length  several 
times  that  of  the  normal  body. 

All  groups  of  cercariae  possess  an  oral  suctorial  organ.  For  the  second 
attachment  organ  there  is  a  variety  of  accommodation.  Undoubtedly  the 
most  advantageously  formed  organ  of  this  second  typo,  is  the  one  found  in  the 
Amphistomata,  where  there  is  a  powerful  suctorial  disc  at  the  posterior  end  of 
the  body. 

Among  the  distomes  there  are  many  types  of  posterior  suctorial  organ, 
ranging  from  those  with  a  prominent  acetabulum  not  far  from  the  caudal 
extremity,  as  in  Stomylotrema  pictum  (Crep.)  (Looss  1899:629),  to  those  with 
a  poorly  developed  acetabulum  more  cephalic  in  position.  In  the  latter  case 
there  are  frequently  found  auxiliary  locomotor  organs,  such  as  those  in  the 
posterior  pockets  of  the  xiphidiocercariae.  In  some  species  there  is  only 
a  suggestion  of  a  paired  suctorial  organ,  as  in  the  larvae,  Cercaria  crenata  (Fig. 
55),  and  C  diaphana  (Fig.  76).  In  others  there  is  the  additional  spinose 
complement  (C.  glandulosa,  C.  dendritica,  and  C.  micropharynx).  These  spines 
are  of  important  fimction  on  rough  surfaces  where  the  disc  can  take  hold 
with  difficulty.  Altho  there  is  considerable  difference  in  the  rapidity  of 
movement  of  the  various  species  studied,  C.  glandulosa  was  by  far  the  most 
rapid  in  movement  of  all  the  cercariae  observed.  The  spinous  outgrowth  of 
the  acetabulum  is  of  advantage  in  locomotion,  catching  hold  where  the  un- 
armed sucker  can  not  operate  (C  glandulosa,  Fig.  60 ;  and  C.  gracillima,  Fig.  142). 

Muscular  development  in  the  holostome  larva  is  confined  entirely  to  the 
suctorial  apparatus,  since  there  is  no  distinct  tail  portion.  This  type  of  sucker 
is  derived  from  the  distome  type.  With  the  translocation  of  the  genital  opening 
to  the  posterior  end  of  the  body,  the  primitive  genital  pore  has  come  to  be  used 
as  an  accessory  suctorial  organ  (Cercaria  ptychocheilus,  Fig.  47).  The  most 
unique  modification  is  found  in  the  tetracotyle  type.  Here  there  have  arisen 
two  lateral  accessory  suctorial  grooves  (Fig.  41),  and  lappet  modifications  of 


251  LIFE  HISTORY  OF  TREMATODES— FAUST  25 

the  acetabulum.  All  of  these  come  to  be  enclosed  in  a  common  pocket  which 
acts  as  a  large  sucking  cup  (Fig.  40).  There  is  practically  no  locomotion  in 
these  species,  since  movement  is  confined  almost  exclusively  to  the  sucking 
reflex. 

In  the  monostome  no  acetabulum  is  present,  yet  the  cercaria  performs 
the  processes  of  locomotion  par  excellence.  The  pair  of  posterior  locomotor 
organs  replaces  the  acetabulum  in  the  measuring  worm  movement.  In  Cer- 
caria pellucida  and  C.  konadensis,  as  well  as  in  C.  urbanensis  Cort,  these  organs 
consist  of  posterior  inpocketings  of  the  integument.  In  C.  imbricata,  Looss 
(1896,  Fig.  151)  there  is  an  internal  pocket.  In  C  ephemera  Nitzsch  (Ssinitzin, 
1905,  Fig.  75,  76)  there  are  hook-shaped  spines.  Cort  (1915:15)  finds  that 
they  "  apparently  have  no  suctorial  function,  since  no  muscles  are  present  and 
the  central  cavity  contracts  while  the  projection  is  extended."  A  careful 
study  of  living  and  preserved  specimens  of  C.  pellucida,  C.  konadensis,  and 
C.  urbanensis  shows  that  these  three  American  species  have  no  spinose  or 
other  integumentary  modifications.  However,  their  function  is  found  to  be 
distinctly  suctorial,  and  not  "analogous  to  setae,"  as  Cort  believes.  Typical 
drawings  for  the  locomotor  organs  of  any  of  these  three  species  are  shown 
(Figs.  16, 17).  As  will  be  seen  in  figure  16,  there  are  four  muscles  which  are 
attached  to  the  pockets.  By  a  contraction  of  the  pair  xx  the  pocket  disc 
is  applied  to  the  surface  of  the  contact  body;  by  a  relaxation  of  xx  and  a  con- 
traction of  yy  the  pocket  is  released  and  pulled  forward  by  the  general  bodily 
contraction.  This  has  been  observed  repeatedly  in  so  convincing  a  manner 
that  it  leaves  no  doubt  as  to  the  structure  or  function  of  the  organ.  In  addition, 
in  C.  konadensis  (Fig.  21)  a  group  of  glands  just  anterior  to  the  locomotor 
pockets  pour  out  a  mucous  secretion  at  the  time  when  the  disc  is  applied 
to  the  contact  organ.  The  locomotor  pockets  perform  a  similar  function 
and  in  a  similar  manner  to  that  of  the  secondary  suctorial  disc  or  acetabulum 
of  amphistome  or  distome,  altho  these  organs  are  in  no  sense  homologous. 
The  significance  of  the  spines  in  connection  with  the  caudal  locomotor 
pockets  of  distomes  has  been  regarded  by  Leuckart  (1886:128)  as  deserving 
special  consideration.  In  Cercaria  armata  he  considers  them  as  serviceable 
in  keeping  the  tail  attached  to  the  body  after  the  constriction  between  the 
two  parts  has  become  deep.  Looking  into  the  phylogenetic  significance  of 
the  spines  of  the  same  cercaria  species,  Ssinitzin  (1911:68)  regards  them  as 
indicating  a  bifid  ancestral  appendage  of  a  caudal  nature.  In  view  of  the 
fact  that  these  pockets  actually  function  similarly  to  the  locomotor  pockets 
of  the  monostomes,  and  are  more  than  likely  the  ancestors  of  the  monostome 
type  of  pocket  (Fig.  12),  it  seems  hardly  worth  while  to  find  a  more  obscure 
meaning  in  the  structures. 

The  tail  is  the  portion  of  the  cercaria  showing  preeminently  the  adaptation 
of  the  organism  to  free-swimming  life.  In  such  forms  as  C.  setifera  (Monticelli, 
1914),  C.  pennata  and  C.  plumosa  (Ssinitzin,  1911,  Figs.  76-79),  the  prolonged 
free-swimming  existence  has  given  rise  to  setae,  spines  and  scutes. 


26  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [26 

The  tail  arises  as  a  median  posterior  protuberance,  bilaterally  symmetrical, 
and  is,  according  to  the  views  of  Ssinitzin,  phylogenetically  a  paired  organ. 
This  thesis  is  supported,  in  part  at  least,  by  the  fact  that  the  excretory  trunks 
arise  as  paired  organs  in  both  the  body  and  the  tail.  In  the  furcocercariae 
the  caudal  tubules  remain  separate  in  the  rami  of  the  tail  and  also  in  the 
"eyelet  anastomosis"  at  the  junction  of  the  body  and  the  tail.  There  devel- 
ops in  the  tail  the  usual  complement  of  muscles,  a  transverse  layer  externally 
and  a  longitudinal  group  more  median.  Within  the  cylinder  of  muscles  is  the 
group  of  parenchyma  cells  surrounding  the  excretory  tubule. 

In  the  tails  of  distome  cercariae  (Figs.  99,  133)  the  excretory  vessel  is  a 
paired  structure,  separated  in  the  middle  by  a  parenchymatous  partition  with 
one  or  two  nuclei  in  each  section  of  7  /z  thickness.  Some  schistosomatid  larvae 
have,  in  addition,  eleven  or  twelve  pairs  of  oblong  cells  just  lateral  to  the 
excretory  vessel.  The  tail  of  the  monostome  is  characterized  by  extra  large 
longitudinal  muscles  with  prominent  nuclei.  The  portion  within  the  longi- 
tudinal muscle  cyHnder  differs  in  structure  in  individual  species.  In  C.  pellu- 
cida  there  is  one  ring  of  very  large  parenchyma  cells  situated  around'  the 
excretory  vessel.  There  are  eight  to  ten  cells  to  each  transverse  plane  of  7/i. 
In  C.  konadensis  and  C.  urhanensis  there  are  glandular  cells  within  the  paren- 
chyma ring;  they  are  large  and  crowded  with  granules.  In  both  of  these  species 
(Figs.  25,  32)  these  cells  are  arranged  in  six  paired  groups.  In  C.  konadensis 
there  are  many  cells  to  each  member  of  the  group,  arranged  in  pyramidal 
fashion  with  the  apex  directed  distally.  Thus  the  largest  cells  in  each  group 
(Fig.  27)  are  proximal.  These  cells  He  next  to  the  excretory  vessel.  Cort 
has  described  the  cells  of  C.  urhanensis  thus:  "extending  the  length  of  the 
tail  and  forming  a  core  are  two  rows  of  long  cells  which  are  close  together  and 
have  their  long  axes  parallel  with  the  length  of  the  tail.  .  .  ,  They  are  full 
of  heavy  staining  granules.  .  .  There  is  nothing  suggestive  of  the  possible 
function  of  these  cells. "  He  has  failed  to  observe  the  exact  number  of  these 
cells  (six  pairs)  and  is  in  error  in  considering  them  as  a  core  extending  the 
whole  length  of  the  tail,  for  they  alternate  with  non-glandular  tissue  in  about 
half  of  the  extent  of  the  organ.  Their  structure  is  probably  glandular.  In 
C.  urhanensis  these  cells  arise  from  undififerentiated  parenchyma  cells  (Fig.  2>2>). 
They  soon  appear  as  falciform  cells  in  trans-section  (Fig.  34),  separated  in 
a  median  sagittal  plane  by  a  partition  arising  between  two  intermediate 
parenchyma  cells,  which  soon  differentiate  into  a  muscular  lamina.  The 
lamina  arises  before  the  excretory  tubules  differentiate  as  distinct  lumina 
among  the  parenchyma  cells.  Thus  the  bilateral  symmetry  along  the  median 
sagittal  plane  is  well  show^n.  The  excretory  vessel  is  single  in  the  mature 
C.  pellucida  and  C.  konadensis,  but  remains  paired  in  C.  urhanensis. 

Looss  (1893:24-28)  cites  the  epithelial  cells  of  the  tail  of  cercariae  as  good 
examples  of  "  Blasenzellen, "  where  all  cell  elements  of  the  mesenchyme  usually 
become  "  Blasenzellen  ",  and  where  no  true  glands  take  their  place.  The  study 
of  C.  konadensis,  C.  urhanensis,  and  C.  gracillima,  shows  that  axial  cell  glands 
are  present,  and  that  they  are  derived  from  the  parenchyma,     Moreover 


27]  LIFE  HISTORY  OF  TREMATODES— FAUST  27 

where  these  special  gland  cells  are  not  present,  as  in  C.  pellucida,  the 
parenchyma  cells  are  more  vesicular  than  where  they  are  present.  The  writer 
is  in  accord  with  Looss's  view  that  there  are  no  indifferent  cells  remaining 
in  the  tail.  Hence  the  tail,  when  separated  from  the  body,  can  not  meta- 
morphose into  a  sporocyst  or  redia,  as  the  older  writers  believed  (Pagenstecher, 
1857:15). 

INTEGUMENT 

The  covering  of  trematodes  and  cestodes  has  been  the  subject  of  con- 
siderable controversy.  Four  main  theories  have  been  proposed.  The  Bloch- 
mann  theory  (1896)  assumes  that  the  cuticula  of  trematodes  and  cestodes  is 
a  true  morphological  cuticula  secreted  by  the  hypodermis,  as  in  other  inver- 
tebrates. A  second  theory,  presented  by  Brandes  (1892),  postulates  that 
trematodes  have  no  subcuticula  in  the  true  sense  of  the  term,  and  what  has 
been  considered  as  such  is  nothing  more  than  the  true  parenchymatous  con- 
nective tissue.  Nevertheless,  the  body  covering  is  a  true  cuticula,  secreted 
by  special  glandular  cells  of  epidermal  origin  just  beneath  the  cuticula.  The 
presence  of  apparent  nuclei  in  the  cuticula  has  revived  the  old  idea  of  Wagener 
that  the  cuticula  is  a  metamorphosed  epithelium.  Goto  has  subscribed  to 
this  theory  in  his  study  of  ectoparasitic  trematodes  (1894:6-13),  defining 
three  layers,  an  outer  cuticula,  a  subcuticula,  and  a  basement  membrane. 
This  is  also  the  interpretation  Monticelli  has  put  on  the  body  investment  of 
Cotylogaster  michaelis  (1892:189),  which  he  claims  to  possess  an  "ectoderma 
sinciziale  di  aspetto  cuticuloide. "  More  recently  Gary  (1909:646)  has  ad- 
vocated this  view.  Pratt  (1909:721)  is  incHned  toward  Leuckart's  theory 
that  the  cuticula  is  of  parenchymatous  origin,  a  derivative  of  the  peripheral 
portion  of   the  parenchyma. 

The  species  of  larval  trematodes  studied  by  the  writer  are  uniform  in 
showing  that  the  epidermal  layer,  developing  into  a  syncytium  in  many  cases, 
is  present  in  the  early  stages  of  the  sporocyst,  redia,  and  cercaria.  In  the 
parthenitae,  especially  in  the  redia,  this  layer  may  persist  until  the  germ 
balls  within  are  ripe  and  ready  to  escape.  In  the  cercaria  the  epidermal 
tissue  is  present  in  early  life  as  a  syncytial  layer  investing  the  larva.  In  the 
mature  cercaria  it  is  sloughed  off.  The  "cuticula,"  when  present,  arises 
from  below  the  epidermis.  It  is  a  discrete  layer  underneath  the  epidermis, 
or  it  impregnates  the  epidermis  from  below.  In  the  latter  case  the  nuclei  are 
always  superficial,  usually  rising  above  the  surface  as  small  tuberosities. 

In  the  monostome  group,  the  redia  possesses  a  syncytium  of  ectodermal 
cells  impregnated  here  and  there  with  granules  of  a  secretory  nature.  The 
cercaria  develops  a  well-defined  epidermis  which  later  (Fig.  37)  becomes 
syncytial  and  is  sloughed  off.  Underneath  this  the  "cuticula"  is  distinctly 
cut  off  from  the  epidermis  on  the  outside  and  from  the  mesodermal  tissue 
beneath.  Among  the  latter  are  the  special  parenchyma  cells  with  aciculate 
pseudopodia,  corresponding  to  Blochmann's  "Epithelzellen"  (1896:7).  These 
differentiated  parenchyma  cells  have  no  connection  with  the  "cuticula"  in 


28  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [28 

the  developing  or  mature  cercaria  of  this  group.  A  non-nucleated  epidermis 
is  shown  in  the  process  of  sloughing  off  for  the  hemistome  cercaria  (C 
ptychocheiliis,  Fig.  54) .  Underneath  is  a  distinct  layer  of  ' '  cuticula. ' '  B  eneath 
the  "cuticula "  is  a  lining  of  transverse  and  longitudinal  muscle  fibers.  Median 
to  the  complexes  of  the  longitudinal  muscles  are  the  complexes  of  the  con- 
nective tissue.  The  whole  structure,  from  the  inner  wall  of  the  "cuticula" 
thru  to  the  free  parenchyma,  is  infiltrated  and  bound  together  into  a  single 
mass  by  a  mucoid  secretion.  This  secretion  is  indifferent  to  stains.  The  epi- 
theHal  cells  of  the  complex  send  out  long  processes  toward  the  integument,  so 
that  the  processes  penetrate  into  the  latter.  These  cells  suggest  gland  cells, 
concerned  with  the  secretion  of  the  "cuticula."  They  are  not  potentially 
different  from  the  underl>'ing  parenchyma. 

Among  the  distome  larvae  the  writer  has  studied  the  "cuticula"  problem 
for  echinostomes,  schistosomes,  and  xiphidiocercariae.  The  redia  of  C.  trisole- 
nata  possesses  an  ectodermal  reticulum  in  which  are  foimd  large  vesicular 
nuclei.  This  covering  is  impregnated  with  large  granules  which  are  indifferent 
to  stains.  In  the  cercaria  of  this  form  (Figs.  128-133),  there  is  an  ectodermal 
layer  present,  very  thin,  with  the  nuclei  arising  from  the  surface  as  minute 
tuberosities.  Beneath  this  is  the  thick  layer  of  "cuticula."  The  epidermis 
has  been  lost  in  the  tail.  No  "Epithekellen"  are  visible  in  the  mesenchyme 
complex.  For  the  schistosome  larva,  C.  gracillima,  there  are  definite  nuclei 
present  as  minute  papillations  rising  above  the  surface  of  the  epidermal  layer. 
The  sporocyst  of  this  form  has  no  "cuticula."  The  body  wall  consists  of 
a  single  layer  of  ectoderm  cells,  arranged  end  to  end,  the  nuclei  of  which  are 
oval  to  subspherical.  In  the  distome,  C.  glanduLosa,  the  sporocyst  wall  is 
composed  of  a  single  layer  of  epidermal  cells,  with  falciform  nuclei.  In  the 
cercaria  the  epidermis  is  present  only  in  individuals  where  the  taU  is  still 
attached.  Here  nuclei  are  present  in  the  peripheral  layer  of  the  body,  but 
are  not  foimd  in  the  covering  of  the  tail.  The  "cuticula"  is  a  thin  envelope 
around  the  circular  layer  of  muscles. 

The  study  of  these  trematodes  with  reference  to  the  problem  of  the  integu- 
ment has  led  the  writer  to  set  aside  the  view  that  the  "cuticula"  is  ectodermal 
in  origin,  because  the  ectoderm  is  superficial,  lying  outside  the  "cuticula." 
The  impregnation  of  this  layer  with  cuticular  granules  might  lead  one  to  be- 
lieve that  the  two  layers  are  one,  but  the  earlier  history  of  the  layers  shows 
that  this  conception  is  erroneous.  No  hypodermis  is  f  oimd  in  any  of  the  species 
studied.  Consequently  the  Blochmann  theory  can  not  hold  for  these  species. 
No  special  gland  cells  have  been  foimd  to  support  in  its  entirety  the  theor}'  of 
Brandes.  On  the  other  hand  the  evidence  of  this  study  points  to  the  sus- 
taining of  Leuckart's  theory  of  the  parenchymatous  origin  of  the  basement 
membrane  on  the  following  grounds.  1)  In  all  the  species  the  basement  mem- 
brane arises  from  tissue  beneath  the  ectodermal  layer.  2)  In  all  cases  where 
there  is  an  ectodermal  layer  only  (in  sporocysts),  no  basement  membrane  is 
found.  3)  The  heaviest  layer  is  foimd  in  species  where  the  parenchj-ma  has 
a  widely  diversified  potency,  such  as  salivary,  cystogenous,  locomotor  and 


291  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  29 

mucin  glands,  4)  The  "Epithelzellen"  of  the  monostomes  and  holostomes 
(Figs.  37, 54)  are  characterized  by  large  vesicular  nuclei  and  vacuolated  cyto- 
plasm, similar  to  the  "Blasenzellen"  of  Schwarze  (1886)  and  Looss  (1893). 
They  are  modified  parenchyma  cells  differing  from  the  underlying  layers  not 
in  potency  but  in  location.  5)  As  the  secretory  cells  for  the  basement  mem- 
brane, these  parenchyma  cells  have  developed  long  acicular  pseudopodia 
toward  the  membrane  and,  in  the  larval  holostomes,  have  penetrated  into  it. 
All  of  these  data  point  toward  the  parenchymatous  origin  of  the  basement 
membrane. 

PARENCHYMA 

Soon  after  the  fundaments  of  the  digestive  and  nervous  systems  of  the 
cercaria  are  laid  down,  certain  cells  of  mesodermal  origin  of  the  germ  ball 
become  ovoid  and  are  filled  with  milky  white  granules.  These  are  cystogenous 
cells,  the  "Stabenkornchen"  of  the  German  writers  and  the  "cellules  a 
bS,tonnets"  of  the  French.  They  develop  most  conmionly  in  monostomes, 
amphistomes,  and  such  distomes  as  form  a  heavy  cyst. 

Other  portions  of  the  mesoderm  are  differentiated  as  the  germinal  epithe- 
lium and  the  muscle  layers.  The  remainder  of  the  mesodermal  cells  is  for  a 
considerable  time  potentially  great,  and  remains  undifferentiated  (Looss, 
1893:29).  They  constitute  the  parenchyma.  Looss  has  compared  these 
cells  of  the  mesoderm  to  the  cambium  of  the  plant.  They  are  the  "nicht- 
veranderten  Zellen,"  on  the  multiplication  of  which  depends  the  growth  of 
the  minute  larva  to  the  relatively  large  adult.  As  the  animal  grows  the  cells 
of  this  region  become  more  vesicular,  vacuoles  appear  within  the  cytoplasm, 
and  acidophilous  granules  appear  within  the  cell.  The  intercellular  spaces 
become  more  and  more  prominent.  The  cells  are  held  together  by  bands  of 
ragged  connective  tissue  which,  for  the  most  part,  is  the  outgrowth  of  the 
interstitial  cells.  Within  this  parenchyma  complex  there  appear  large  tubular 
lumina  in  certain  definite  regions,  and,  leading  into  these,  tubes  and  smaller 
tubules.  These  are  the  excretory  tubes;  at  the  ultimate  ends  of  these  are 
found  the  capillaries  and  the  flame  cells  (Looss,  1892:162;  Thomas,  1883:116- 
118).  In  the  schistosome  cercariae  studied  the  main  group  of  cilia  is  not  at  the 
extreme  ends  of  the  ducts,  but  in  a  pocket  in  the  posterolateral  part  of  the 
main  trunks  (Figs.  143,  145).  It  is  of  importance  to  emphasize  here  that 
these  excretory  trunks  and  tubes  are  not  lined  by  a  wall  of  specialized  cells, 
but  are  merely  lumina  among  certain  cells  of  the  parenchyma.  It  seems 
highly  probable  that  Looss 's  view  is  correct  as  regards  the  flame  or  "Trichter, " 
that  it,  too,  is  an  intercellular  lumen,  into  which  the  parenchyma-cell  cilia 
protrude,  and  that  it  is  not  in  a  hoUowed-out  cell.  The  cilia  are  definitely 
outgrowths  of  the  single  cell  at  the  head  of  the  capillary  (Fig.  138),  a  cell 
which  is  differentiated  from  the  sister  cells  of  the  parenchyma  by  the  possession 
of  a  much  smaller  nucleus  and  densely  granular  protoplasm. 


30  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [30 

MUSCULATURE 

The  muscle  systems  of  the  parthenitae  and  the  cercariae  are  confined, 
for  the  most  part,  to  the  peripheral  and  splanchnic  regions.  The  peripheral 
muscles  consist  of  an  outer  series  of  radial  muscle  fibers  and  an  inner  series 
of  longitudinal  fibers.  A  third  series,  the  dorsoventral,  which  is  common 
in  the  adult  forms,  is  suggested  at  times  in  the  body  of  the  cercaria.  The 
muscles  of  the  intestinal  tract  consist  of  a  longitudinal  and  a  circular  series. 

The  peripheral  system  Ues  directly  beneath  the  basement  membrane.  It 
opens  interstitially  to  permit  the  growth  of  the  processes  of  the  parenchyma 
cells  which  secrete  the  basement  membrane.  The  outermost  layer  is  the  cir- 
cular series.  It  may  consist  of  a  single  band  one  cell  in  thickness  or  it  may  in- 
clude a  cylindrical  band  several  layers  thick  (Figs.  37,  54,  97, 128).  Within  this 
is  the  longitudinal  series.  Usually  here  the  individual  fibers  of  the  bundles 
are  separated  from  one  another  by  a  considerable  interval.  The  fibers  are 
longer  and  fewer  than  those  of  the  circular  series.  A  section  of  an  adult  trema- 
tode  shows,  in  addition  to  these,  an  obUque  series  of  fibers.  These  obHque  fibers 
give  the  appearance  in  section  of  a  diamond  pattern.  In  another  type,  the 
dorsoventral,  the  fibers  run  at  right  angles  to  the  frontal  plane.  In  the  holo- 
stome  cercaria  (Fig.  54)  no  such  series  is  found,  altho  the  longitudinal  series 
is  so  arranged  that  the  fibers  are  on  edge  and  might  be  taken  for  the  dorso- 
ventral series.  The  view  of  Bettendorf  (1897:315,316)  that  the  "Epithelzellen" 
of  Blochmann  are  really  longitudinal  muscles,  can  not  be  considered  vaUd, 
since  in  the  same  sections  the  former  are  indifferent  to  stains  and  the  latter 
are  deeply  stained  by  the  same  methods  of  technic. 

In  the  oral  and  acetabular  suckers  and  frequently  in  the  phar>-nx  there 
exist  the  transverse,  longitudinal  and  obUque  series  of  muscle  fibers,  inter- 
woven into  an  inseparable  complex.  These  are  best  developed  in  the  Am- 
phistomata.  Since  the  redia  which  produces  germ  balls  is  an  adult  and  the  cer- 
caria is  an  inunature  individual,  it  is  not  surprising  that  the  pharynx  of  the 
redia  is  fibrous,  with  few  nuclei  and  large  vacuoles,  while  the  pharjiix  and 
suckers  of  the  cercaria  are  composed  of  cells  practically  undifferentiated.  In 
the  rediae  the  fibers  can  be  traced  to  the  myoblasts. 

The  main  deep-seated  system  of  muscles  for  the  cercaria  consists  of  the 
muscle  band  series  of  the  digestive  tract.  In  the  holostome  (Fig.  54)  an 
additional  muscular  activity  has  been  assxmied  by  the  cirrus  pouch.  Aside 
from  these  no  muscle  striae  are  developed  in  connection  with  the  genitalia  in 
the  larva.  The  ceca  of  the  digestive  tract  are  covered  with  an  outer  and  an 
inner  series.  The  former  are  longitudinal  fibers  and  the  latter  are  circular 
fibers.  This  is  in  conformity  with  the  muscular  layer  studies  made  on 
other  Platyhelminthes. 

Histology  of  the  muscle  cells.  When  Bettendorf  (1897)  showed  the 
connection  between  the  muscle  fibers  and  the  myoblasts  an  important  step 
was  made  in  the  knowledge  of  the  intimate  structure  of  the  trematode  muscle 
cell.    The  present  study  corroborates  Bettendorf 's  work.    The  nuclei  of 


31]  LIFE  HISTORY  OF  TREMATODES— FAUST  31 

the  myoblasts  are  oval  (Figs.  118,  119).  The  cells  very  early  send  out 
long  protoplasmic  strands  along  well  defined  paths.  While  the  processes 
from  the  myoblasts  may  emerge  from  any  part  of  the  cell,  the  longitudinal 
strands  are  always  directed  in  a  longitudinal  plane,  and  the  circular  fibers 
are  always  circular.  A  unique  picture  is  presented  at  the  point  where  the 
furcae  of  the  digestive  tract  arise  (Fig.  118).  Here  there  are  two  anterior 
processes  running  cephalad,  and  three  strands  proceeding  caudad  along  each 
cecum.  The  chromatin  in  the  nucleus  of  the  myoblast  is  usually  confined 
to  the  karyosome. 

^  ARMATURE  OF  THE  TREMATODE 

The  miracidiimi  and  sporocysts  are  not  ordinarily  provided  with  hooks 
or  any  piercing  armature.  The  redia  is  usually  conspicuous  because  of  its  oral 
sucker,  pharynx  and  gut,  and  not  because  of  any  armature.  In  the  cercaria, 
however,  are  found,  even  in  some  of  the  most  delicate  species,  spines  covering 
the  basement  membrane,  especially  in  the  region  of  the  head.  In  the  special 
group  of  the  stylet  cercariae  the  stylet  is  the  larval  organ  which  is  of  specific 
systematic  value. 

It  is  not  a  universal  rule,  however,  that  all  rediae  and  sporocysts  are  un- 
armed. At  times  a  modification  of  the  posterior  wall  of  the  redia  is  produced 
as  in  the  redia  of  C.  biflexa,  where  the  terminal  organ  is  spinose  (Fig.  141). 
Leiper  and  Atkinson  (1915:202)  found  the  second  sporocyst  generation  of 
Schistosoma  japonicum  to  be  covered  with  a  spinous  integument.  More 
conspicuous  is  the  prepharynx  organ  of  the  redia  of  Cercaria  pellucida  (Fig.  7). 
This  organ  is  four-lobed,  and  has  on  the  outer  side  of  each  lobe  long  spines 
projecting  forward  and  small  spines  directed  laterad.  The  use  of  such  a 
weapon  within  the  soft  parts  of  the  host  tissue  produces  untold  injury. 

No  armature  has  been  observed  on  the  body  of  any  monostome  cercaria. 
The  holostome,  Tetracotyle  pipientis  (Fig.  47),  has  a  spinose  covering  over  the 
entire  body  and  special  spines  in  the  region  of  the  acetabulum  and  accessory 
suctorial  grooves.  Spinose  modifications  are  common  in  the  distome  group, 
and  in  some  cercariae,  setiferous  modifications  of  the  tail.  The  types  which 
the  writer  has  examined  have  the  armature  confined  to  the  body.  They  will 
be  discussed  under  the  headings  of  1)  general  body  spines,  2)  spines  of  the 
oral  aperture,  3)  collar  spines  of  the  echinostomes,  and  4)  the  stylet  organ 
of  the  xiphidiocercariae.  In  addition  there  are  the  spines  at  the  posterior 
end  of  the  trunk  in  the  caudal  pockets.  Their  probable  locomotor  function 
has  made  it  necessary  to  consider  them  in  another  place. 

In  many  cercariae  there  is  a  tendency  for  the  entire  bodily  integiunent 
to  become  modified  so  that  the  surface  bristles  with  needle-like  spines.  These 
are  usually  arranged  in  a  regular  diamond  pattern,  and  are  more  fully  devel-  . 
oped  at  the  anterior  end  of  the  body  than  in  the  caudal  portion  (Figure  90). 
This  condition  is  found  in  some  xiphidiocercariae  and  some  echinostomes. 
The  spines  are  always  pointed  forward.  They  are  more  fully  developed  in 
the  anterior  region  of  the  body. 


32  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [32 

Of  a  somewhat  more  limited  distribution  is  the  oral  armature  of  spines 
in  the  schistosomatid  C.  gracillima  (Fig.  142) .  These  spines  are  turned  into  the 
body  with  the  inpocketing  of  the  oral  sucker-pouch,  so  that  the  animal  in  the 
condition  of  contraction  appears  perfectly  aspinose  except  for  the  armature 
of  the  acetabulum.  But  with  its  protrusion  the  oral  sucker  is  crowned  with 
a  sohd  cap  of  spines. 

The  hood  of  spines  of  the  echinostome  group  is  specialized  and  valuable 
in  systematic  work.  It  is  usually  an  incomplete  ring,  consisting  of  a  circlet 
of  spines  around  the  dorsal  side,  extending  ventrad  into  the  middle  half  of 
the  body.  Dietz  (1910)  has  sketched  63  figures  of  spine  characters  and 
numbers  in  his  monograph  on  the  Echinostomidae  of  birds.  The  adult  echi- 
nostomes  of  North  America  have  received  little  attention  and  in  consequence 
of  the  difficulty  in  working  out  the  exact  spine  number  in  the  larva  a  descrip- 
tion of  the  specific  spine  characters  of  the  cercariae  will  not  be  worth  while 
until  more  attention  is  given  to  the  adults  of  the  family. 

The  stylet  is  the  unique  larval  organ  in  the  group  of  the  xiphidiocercariae. 
It  might  be  more  properly  called  a  quill  than  a  stylet,  for  its  value  as  an  organ 
of  piercing  is  questionable  on  account  of  its  frailty  and  frequently  disadvanta- 
geous leverage.  It  is  a  mucoid  structure,  situated  in  the  dorsal  wall  of  the  oral 
pocket,  well  supplied  with  muscles  to  work  it  in  any  direction  anteriad  and 
laterad.  It  is  fully  formed  only  in  the  mature  cercaria,  and  is  carried  into 
the  cyst  (Figs.  84,  85).  Quite  generally  the  stylet  is  recognized  as  of  specific 
systematic  value,  and  is  therefore  figured  in  systematic  descriptions  (Liihe, 
1909:189-200),  but  the  stylets  as  they  are  figured  are  so  generalized  as  to  be 
of  little  value  in  the  identification  of  species.  The  stylet  is  of  specific  value, 
but  this  value  lies  in  the  details  of  the  organ  rather  than  in  the  general  out- 
line.    (See  Figs.  57,  61,  77,  83,  91,  102). 

The  stylet  is  usually  a  weak  organ  mechanically  and  poorly  levered. 
However,  it  is  resistent  to  chemicals  and  indifferent  to  dyes.  The  stylet  of 
Cercaria  glandulosa  is  extremely  delicate,  so  that  it  goes  to  pieces  immediately 
when  a  cover  glass  is  pressed  down  on  a  water-mount  of  the  worm.  The 
stylet,  as  a  rule,  is  hard  to  observe  in  preserved  mounts. 

GLANDS  OF  THE  LARVAL  TREMATODE 

Glandular  organs  in  the  trematode  may  be  distinguished  as  dermal,  salivary, 
mucin,  cystogenous,  genital,  and  locomotor.  The  dermal  glands  are  those 
imbedded  in  the  subdermal  tissues,  are  unicellular,  usually  flask-shaped,  and 
have  a  small  duct  opening  to  the  exterior.  The  saUvary  glands  include  all  of 
the  unicellular  glands  which  open  into  the  digestive  tube.  Mucin  glands  are 
paired,  right  and  left  groups  of  one  to  several  gland  cells  emptying  into  the 
oral  pocket  thru  long  attenuate  ducts.  Since  mucin  is  a  constituent  of  salivary 
glands,  these  glands  are  modified  salivary  glands.  Cystogenous  glands  are 
imbedded  in  the  parenchyma  and  are  usually  filled  with  rhabditiform  granules 
which  superficially  resemble  the  dermal  rhabdites  of  the  Turbellaria  but  are 


33]  LIFE  HISTORY  OF  TREMATODES— FAUST  33 

not  to  be  confused  with  them.  The  cystogenous  glands  function  in  the  for- 
mation of  the  larval  cyst  at  the  time  when  the  transfer  to  the  secondary  or 
definitive  host  is  to  be  made.  Genital  glands,  in  the  sense  employed  here, 
include  only  the  auxiUary  gland  elements  of  the  genital  system  and  do  not 
refer  to  the  sex  glands  themselves.  Locomotor  glands  arise  in  connection 
with  the  locomotor  organs  in  the  posterior  part  of  the  body. 

The  dermal  glands  are  of  adult  significance.  Looss  (1894:125)  has  found 
them  in  all  groups  of  adult  trematodes  studied,  but  he  does  not  later  (1896: 
219,  Fig.  176,  glcu)  record  them  for  any  cercariae  except  C.  vivax  Sons. 
No  dermal  glands  have  been  found  by  the  writer  in  the  course  of  the  present 
study. 

Salivary  glands  are  probably  present  in  all  groups  of  cercariae  and  in 
some  rediae.  In  the  simplest  form  they  are  nothing  more  than  pyriform  cells 
in  the  region  of  the  digestive  tube.  Thus  the  monostome  cercaria,  C.  imbricata, 
described  by  Looss  (1896:195)  as  having  a  pharynx  without  a  bulb,  has  unicell- 
ular glands  massed  around  the  tube  in  the  pharynx  region.  The  f  urcocercariae, 
with  no  true  pharynx,  have  a  similar  group  of  cells  in  the  pharynx  region, 
so  closely  massed  together  as  to  lead  Looss  to  considering  them  a  true  phar)mx 
(1896:220,  Fig.  176,  ph).  In  structure  these  masses  of  glands  in  the  f urco- 
cercariae look  superficially  like  a  pharynx  (Fig.  142),  but  on  cross- 
section  the  cells  of  the  complex  are  found  to  be  unmistakably  glandular 
(Fig.  152). 

A  modification  of  the  type  of  sahvary  gland  just  described  has  been  ob- 
served in  Cercaria  micropharynx,  C.  diaphana,  and  C.  glandtdosa.  In  these 
species  the  cercariae  show  not  only  the  muscular  pharynx,  but  also  a  large 
group  of  gland  cells  around  the  digestive  tract.  In  C  micropharynx  (Fig.  93) 
the  glands  are  prepharyngeal,  grouped  in  a  spherical  mass  around  the  oral 
chamber.  They  are  minute  cells,  about  3/x  in  trans-section.  The  glands  of 
C  diaphana  (Fig.  76)  exhibit  a  maximum  glandular  growth  in  the  vicinity 
of  the  pharynx  proper.  Several  hundred  gland  cells  about  3/i  in  diameter 
surround  the  pharynx.  A  case  of  secretion  along  the  entire  digestive  tract 
is  found  in  C.  glandulosa  (Fig.  60).  In  this  species  the  glands  are  much  larger 
than  in  the  two  preceding  species,  about  6/i  in  cross  section  and  12/i  to  25)u  in 
length.  They  are  formed  along  the  entire  course  of  the  lumen,  from  the  ori- 
fice to  the  blind  end  of  the  ceca,  altho  they  are  best  developed  in  the  region  of 
the  pharynx. 

A  distinctly  different  type  of  gland  is  that  termed  the  "stylet  gland." 
It  is  so-named  because  of  its  frequent  occurrence  coincidently  with  the  stylet 
organ  of  the  xiphidiocercariae.  But  since  it  occmrs,  too,  in  furcocercariae 
and  in  echinostome  cercariae,  where  there  is  no  trace  of  a  stylet,  the  evidence 
supports  the  view  that  this  type  of  gland  is  more  generalized  and  more  primi- 
tive  than   the   stylet  organ. 

These  glands  are  found  in  the  cercariae  of  the  distome  groups  examined 
by  the  writer,  and  in  the  redia  of  the  holostome,  C.  flabelliformis.  They  are 
bilaterally  symmetrical,  lying  outside  the  intestinal  furcae,  behind  the  region 


34  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [U 

of  the  pharynx.  They  open  thru  long-necked  ducts  into  the  oral  pocket.  The 
glands  are  in  masses;  they  vary  in  the  number  of  cells  from  four  in  each  lateral 
mass  of  some  furcocercariae  (Fig.  144),  to  eight  or  ten  in  the  stylet  cercariae, 
while  in  the  echinostomes  they  run  as  high  as  1 10  on  each  side  of  the  esophagus 
(Fig.  134).  In  general  the  cells  are  characterized  by  a  densely  staining  gran- 
ular protoplasm  and  a  highly  refractive  nucleus,  which  remains  hyaline  when 
treated  with  hematoxyhn  dyes.  Most  interesting  is  the  type  presented  in 
Cercaria  crenata  (Fig.  55),  where  there  is  a  differentiation  of  inner  and  outer 
groups  of  the  glands  on  each  side  of  the  gut.  These  groups  have  individual 
canals  to  their  exit  at  the  oral  pocket.  The  outer  series  consists  of  six  glands, 
comparatively  small,  Sfx  to  9/i  in  diameter,  goblet-shaped,  extending  caudad 
to  the  midacetabular  region.  They  are  finely  granular  and  are  best  studied 
in  living  mounts.  The  inner  series  consists  of  five  cells,  two  of  which  are 
situated  just  behind  the  pharynx  and  the  other  three  postacetabular,  thus 
causing  the  inner  series  to  be  divided  into  an  anterior  and  a  posterior  group. 
These  inner  gland  cells  are  llju  to  15ju  in  diameter,  and  coarsely  granular. 
Their  difference  in  structure  suggests  a  functional  difference. 

The  mucin  glands  of  the  redia  of  C.  flabelliformis  are  paired  structures, 
lateral  and  dorsal  to  the  digestive  pouch,  consisting  of  a  single  series  of  six 
cells  which  open  thru  a  common  tube  into  the  pharynx  region  of  the  redia. 
The  cells  are  similar  in  structure  to  the  mucin  cells  of  the  cercariae  of  other 
groups,  altho  no  such  glands  have  been  recorded  from  the  cercariae  of  the 
holostome  group.  Only  one  other  case  has  been  reported  for  the  redia,  that 
for  the  parthenita  of  Cercaria  equitator  by  Ssinitzin  (1911:52,  Fig.  50).  In 
this  redia  the  gland  cells  consist  of  a  single  cell  with  a  wide  duct  to  the  pharynx 
region.  A  similar  pair  of  unicellular  salivary  glands  is  figured  by  Looss  for 
the  miracidium  of  Schistosoma  haematobium  (1896,  Fig.  113,  glcph)  and  by 
Miyairi  and  Suzuki  for  the  miracidium  of  S.  japonicum  (1914,  Taf,  2,  Figs. 
1,  2).  This  occurrence  of  the  mucin  glands  in  the  miracidium,  redia,  and  cercaria 
of  various  groups,  and  the  fact  that  they  pass  into  the  intermediate  host  along 
with  the  larva  (La  Rue,  1917),  show  that  these  organs  are  of  fundamental 
importance  in  the  economy  of  the  worm. 

That  these  glands  are  of  more  specific  character  than  the  ordinary  salivary 
and  epidermal  cells  of  the  trematodes  is  demonstrated  by  their  differential 
staining  reaction.  The  usual  hematoxylin  dyes  show  a  great  nimiber  of 
granular  protein  inclusions.  Recently  La  Rue  (1917)  has  shown  that  these 
glands  in  Cercaria  marcianae  have  "mucus"  in  their  ducts,  because  of, the 
staining  reaction  with  toluidin  blue  and  thionin.  However,  since  the  glycopro- 
tein of  salivary  digestion  is  mucin  (Mathews,  1915:323),  it  is  more  exact  to 
designate  these  structures  as  mucin  glands. 

A  t3^e  of  gland  undoubtedly  common  to  all  cercariae  is  the  cystogenous 
gland.  It  is  a  unicellular  organ  in  the  parenchyma  just  beneath  the  integument. 
In  some  groups  this  cell  may  be  small  and  in  the  midst  of  parenchyma 
cells  (C  glandulosa,  Fig.  62).  In  other  groups  the  cystogenous  cell  is  very 
large  and  conspicuous  as  in  the  species  C  pellucid  a   (Fig.  14),  C  dendritica 


35]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  35 

(Fig.  85),  and  C.  trisolenata  (Fig.  132).  The  material  within  the  cyst  cell  is 
usually  milky,  semi-opaque,  either  homogeneous  or  granular.  In  most  cases 
the  contents  consist  mainly  of  the  rhabditiform  granules,  which  are  indif- 
ferent to  dyes.  These  granules  are  not  attacked  by  weak  acids  or  alkalies, 
but  are  digested  by  strong  acids  or  bases.  It  seems  probable  that  they  are 
of  a  derived  protein  nature. 

The  formation  of  the  cyst  varies  in  the  types  studied.  In  the  majority 
of  the  species  the  cyst  is  a  firm  envelope  with  a  free  space  around  the  embryo, 
more  or  less  filled  with  a  watery  fluid  (Figs.  41,  84,  118).  On  the  other  hand, 
some  of  the  cysts  are  more  mucoid  in  structure,  with  a  granular  viscous  inner 
portion  and  an  outer  jell  (Fig.  11), 

The  method  of  encystment  differs  in  different  species.  In  the  monostome 
where  the  encystment  is  rapid  and  an  entire  lot  of  mature  cercariae  encysts 
in  two  or  three  minutes  after  they  are  freed  from  the  redia,  the  process  is  so 
rapid  that  the  tail  is  not  entirely  cut  off  until  the  major  portion  of  the  cyst 
as  formed  (Figs.  9-11).  Where  the  time  of  encystment  is  considerably  longer, 
OS  in  C.  trisolenata  and  C.  dendritica,  the  tail  is  discarded  long  before  the  process 
of  encystment  actually  begins.  Encystment  is  an  adaptation  on  the  part 
of  the  larva  to  the  change  in  environment.  In  two  cases  studied  it  takes  place 
within  the  liver  of  the  primary  host  (C.  micropharynx  and  C.  biflexa).  It  is 
highly  probable  that  in  these  forms  encystment  was  the  result  of  temperature 
stimuli,  since  the  worms  were  secured  in  November  when  the  winter  had 
already  set  in.     It  is  apparently  an  adaptation  for  "wintering  over." 

In  only  one  group,  the  furcocercariae,  has  there  been  no  record  of  encyst- 
ment of  the  cercaria.  Here  the  tail  is  dropped  only  under  the  pressure  of  the 
cover  slip  or  when  the  worm  begins  to  disintegrate.  La  Valette  (1855:34) 
expresses  this  condition  for  his  forms  when  he  writes  of  the  larvae:  "Cercariae 
cystibus  non  indutae  in  animalium  vertebratorum  intestinis  pereunt." 

The  phenomenon  of  encystment  is  one  which  has  been  observed  by  many 
investigators.  It  has  been  seen  and  described  very  accurately  by  La  Valette, 
Moulinie  (1856),  Pagenstecher  (1857),  and  a  long  line  of  later  investigators. 
Moulinie  refers  to  the  studies  of  earlier  workers  on  encystment,  mentioning 
von  Siebold  (1835)  and  Steenstrup  (1842).  But  the  credit  for  the  first  record 
of  encystment  undoubtedly  belongs  to  Nitzsch  (1807).  Later  (1816)  this 
writer  records  his  observations  on  the  encystment  of  Cercaria  ephemera. 
The  review  of  Nitzsch  in  Isis  describes  the  process  of  decaudation  and  en- 
cystment as  observed  by  Nitzsch,  and  shows  that  this  worker  expected  the 
cyst  to  develop  the  following  year.  Fantham  's  criticism  of  Nitzsch  is  essen- 
tially unjust  (1916:12),  since  Nitzsch  considered  the  cyst  to  be  dormant  ands  set 
dead. 

The  process  of  encystment  has  been  described  in  detail  by  Thomas  in 
his  work  on  Fasciola  hepatica  (1883:129).  Encystment  here  conforms  to  the 
rapid  type  described  for  the  monostome  C.  pellucida.  "The  tail  is  sometimes 
shaken  off  before  encystment  begins,  but,  as  a  rule,  the  tail  remains  in  con- 
nection with  the  body  during  the  process,  and  continues  to  be  energetically 


36  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [36 

lashed  from  side  to  side,  until  finally  a  more  vigorous  movement  detaches 
it.  The  whole  process  is  very  rapid,  and  in  a  few  minutes  a  layer  of  consid- 
erable thickness  is  formed,  whilst  its  substance  begins  to  harden. " 

EXCRETORY  SYSTEM 

The  excretory  system  is  the  most  dehcate  of  the  four  important  systems 
o  the  trematode.  It  can  be  worked  out  with  precision  in  the  Uving  animal, 
but  in  preserved  material  it  is  impossible  to  find  more  than  the  main  trunks 
of  the  system.  In  all  of  the  cercariae  and  parthenitae  described  in  this  paper 
the  excretory  systems  have  been  studied  from  living  material.  Altho  there 
are  many  individual  differences  within  groups,  yet  the  fundamental  uniformity 
of  groups  is  evident. 

A.  The  Monostomata.  The  main  features  of  the  excreton,-^  system  of  the 
Monostomata  are  the  two  main  trunks  arising  from  a  common  point  just  behind 
the  median  eye-spot  or  median  pigment  center,  and  proceeding  posteriad  and 
laterad  to  the  posterior  part  of  the  body,  where  they  join  one  another  in  the 
common  vesicle.  The  bladder  opens  to  the  outside  thru  the  excretory  pore, 
which  is  not  terminal  but  slightly  dorsal. 

The  main  excretory  trunks  are  filled  with  large  refractor}'  granules,  more 
extensively  described  on  p.  42.  The  continuous  circuit  of  the  system  provides 
for  the  transfer  of  granules  and  other  waste  products  from  right  to  left  and 
reversely,  dependent  on  the  contraction  and  expansion  of  the  several  parts  of 
the  animal. 

The  bladders  of  the  various  species  differ  considerably  in  size  and  structure, 
but  as  a  whole  they  may  be  placed  in  two  sub-groups.  In  the  trioculate  forms, 
such  as  Cercarin  pdlucida,  in  dorsal  view  the  bladder  is  distinctly  trilateral 
when  relaxed,  with  the  excretory  pore  at  the  posterior  horn.  This  same  type 
is  found  in  C.  ephemera  Nitzsch  (Ssinitzin,  1905,  Fig.  76),  and  in  C.  imbricata 
Looss  (18%,  Fig.  148),  and  also  in  C.  zostera  (Ssinitzin  1911,  PI.  1,  Figs.  14, 
15). 

In  action,  however,  due  to  the  muscular  movements  of  the  posterior  portion 
of  the  body,  the  anterior  portion  of  the  bladder  may  seem  to  be  a  separate 
organ  opening  into  the  bulbous  posterior  portion  of  the  vesicle  thru  a  con- 
stricted area.  In  the  binoculate  tj'pes,  on  the  other  hand,  the  bladder  is  spheri- 
cal, with  the  excretory  trunks  emptying  into  the  extreme  lateral  reaches  of  the 
vesicle.  The  excretory  pore  in  these  species  is  subterminal  rather  than  termi- 
nal. The  only  binoculate  species  known  are  C.  lophocerca  (de  FiUppi,  1857,  PI. 
1,  Fig.  3),  C.  itrbanensis  (Cort,  1915,  Fig.  5),  and  C.  konadensis.  Lebour 
(1907:443,  PL  X,  Fig.  B)  describes  the  bladder  of  C.  lophocerca  as  semilunar, 
but  from  her  figure  it  appears  more  reniform  than  lunar.  Cort  does  not 
describe  the  shape  of  the  bladder  of  C.  urbanensis,  or  state  its  size.  The  writer 
has  found  it  to  measure  50/i  to  60/i  in  median  sagittal  line  and  60ju  in  transverse 
section  for  preserved  material.  The  excretor)'^  pore  of  this  species  is  large, 
some  20^1  in  diameter;  it  is  weakly  muscular  (Fig.  35).  In  C.  konadensis  (Fig. 
29)  the  bladder  is  smaU,  14)ii  to  IS/x  in  diameter.  The  excretor)'  pore  is  cor- 
respondingly small,  3n  to  4^i  in  diameter,  and  weakly  muscular. 


37]  LIFE  HISTOR Y  OF  TREMA  TODES—FA UST  37 

The  excretory  system  in  the  tail  of  monostomes  is  simple.  It  consists 
of  a  median  tubule,  with  tributary  laterals,  which  swell  in  the  proximal 
region  and  empty  into  the  common  bladder  of  the  trunk. 

B.  Holostomata.  The  excretory  systems  of  Holostomidae  and  Hemi- 
stomidae  are  sufficiently  different  to  require  separate  treatment. 

1.  Holostome  type.  No  accurate  or  detailed  description  of  the  tetracotyle 
type  of  excretory  system  exists.  De  Filippi  (1857,  Fig.  26)  has  pictured  two 
laterals  for  C.  vesiculosa,  arising  from  nimoierous  tubules  in  the  anterior  part 
of  the  body.  The  connection  of  these  tubes  in  the  region  of  the  bladder  is  not 
clear.  Altho  his  sketch  was  made  ''to  show  particularly  the  lateral  vessels," 
it  gives  no  adequate  conception  of  the  fundamental  vessels  of  the  system. 
Brandes  (1891:569)  merely  states  that  the  "system  reaches  into  all  parts  of 
the  cone;  an  especially  large  canal  passes  longitudinally  thru  the  anterior  wall 
of  the  cone. "  Only  a  faint  suggestion  of  the  system  is  figured  by  Rosseter 
(1909,  Fig.  17),  for  Holostomum  excisum  (von  Linstow).  Brown  (1899,  Fig, 
11)  has  worked  out  an  interesting  but  unusual  type.  In  view  of  the  lack  of 
definite  data  concerning  the  excretory  vessels  of  the  holostomid  group,  it 
seems  advisable  to  describe  the  system  for  the  species  Cercaria  flabelliformis. 

The  excretory  system  of  Cercaria  flabelliformis  is  shown  in  figure  39.  At  the 
extreme  posterior  end  of  the  worm,  situated  slightly  dorsally,  is  the  excretory 
pore.  It  is  the  opening  of  a  relatively  small  bladder  no  larger  than  the  pore 
itself.  At  its  antero-lateral  horns  two  large  trunks  arise,  considerably  inflated 
in  their  posterior  portion.  They  may  be  traced  forw^ard  along  the  inner 
reaches  of  the  digestive  ceca  until  they  reach  a  place  about  two-fifths  the  dis- 
tance from  the  anterior  end  of  the  larva.  Here  a  transverse  canal  is  found, 
with  a  median  connection  between  the  two  trunks,  and  lateral  transverse 
tubules.  The  lateral  tubules  drain  the  part  of  the  larva  posterior  and  lateral 
to  them.  Between  them  and  the  main  longitudinal  trunks  are  found  a  great 
number  of  anastomoses.  Anterior  to  the  median  transverse  canal  the  tubules 
spread  out  in  fan-like  arrangement,  running  to  the  sides  and  front  of  the  worm. 

Apparently  this  system  was  originally  distome  in  character,  but  was  made 
over  to  suit  the  needs  of  a  modified  distome  larva.  The  longitudinals  are 
clearly  those  of  the  Y-type  so  common  to  the  excretory  system  of  the  distomes. 
On  the  other  hand,  the  transverse  tubes  and  the  anastomoses  of  the  postero- 
lateral reaches  are  new  structures. 

The  entire  system  is  filled  with  minute  refractory  granules  which  facilitate 
the  tracing  of  the  courses  of  the  various  vessels. 

2.  Hemistome  type.  This  type  has  been  worked  out  in  faithful  detail 
both  in  the  larva  (Diplostomulum)  and  in  the  adult.  Hence  a  discussion  of 
the  excretory  system  of  C.  ptychocheilus  will  be  limited  to  the  points  of  diver- 
gence from  the  previously  described  species. 

The  earliest  larvae  of  this  group  to  be  accurately  figured  are  Diplostomulum 
clavatum  (Nordmann)  and  D.  volvens  (Nordmann)  (1832,  Taf.  II-IV).  From 
the  elongated  bladder  there  arises  a  bicornuate  structure  which  proceeds 
forward  and  outward  for  a  short  distance.     A  bifurcation  of  each  cornu  then 


38  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [33 

takes  place,  so  that  there  are  two  pairs  of  vessels  to  proceed  forward,  an  inner 
and  an  outer  pair.  They  run  forward  to  a  plane  in  front  of  the  middle  of  the 
body,  where  they  unite  and  run  cephalad  as  a  single  vessel.  A  transverse 
vessel  is  found  posterior  to  this  union;  this  vessel  connects  the  two  sides  of 
the  system.  Brandes'  diagram  for  the  excretory  system  of  D.  abbreviaium 
(1891,  Taf.  39,  Fig.  17)  differs  from  this  type  only  in  the  details  and  not  in 
the  main  features. 

The  system  of  Cercaria  ptychocheilus  (Fig.  49)  has  a  long,  attenuate  non- 
muscular  bladder  dorsal  to  the  posterior  genital  apparatus.  It  does  not  pair 
but  gives  off  a  single  median  longitudinal  vessel,  which  proceeds  forward  to 
the  midacetabular  region,  where  it  gives  off  the  transverse  vessel.  The  median 
longitudinal  trunk  then  runs  forward  to  the  origin  of  the  ceca.  Here  it  gives 
rise  to  three  antero-lateral  vessels.  These  bend  outward  and  backward,  with 
numerous  anastomoses,  and  finally  imite  with  the  lateral  traces  of  the  trans- 
verse vessel.  The  outer  reaches  of  the  transverse  vessel  give  rise  to  many 
anastomoses  which  are  conspicuous  in  the  postero-lateral  portion  of  the  body. 

The  fundamental  vessels  of  the  holostome  tv-pe  are  the  paired  laterals  and 
the  transverse  vessel.  Anastomoses  and  modifications  have  altered  the 
system  appreciably,  but  not  beyond  the  ability  to  recognize  in  them  a  conmion 
type  underlying  the  system,  probably  reducible  to  the  Y-type  of  the  distomes. 

The  entire  system  contains  many  mediimi-sized  refractor\'  granules  which 
oscillate  back  and  forth  thru  the  vessek  at  every  movement  of  the  animal. 
By  imusual  contraction  of  the  worm,  the  granules  are  forced  into  the  bladder 
and  out  thru  the  excretor}^  pore. 

C.  Distomata.  The  distome  cercaria  has  a  simple  type  of  excretory 
system,  consisting  of  a  posterior  median  bladder  with  two  lateral  longitudinal 
vessels  in  the  body  of  the  cercaria  and  a  median  longitudinal  vessel  in  the  tail. 

1.  The  xiphidiocercariae.  The  excretory  system  of  the  stylet  cercariae 
consists  of  a  bladder,  usually  muscular,  and  a  pair  of  lateral  longitudinal 
vessels  which  arise  from  lateral  cornua  of  the  bladder.  The  primitive  lateral 
system  consists  of  three  tubules,  which  emerge  from  the  common  lateral  soon 
after  the  latter  leaves  the  bladder.  One  of  these  tubules  proceeds  posteriad, 
while  the  other  two  run  forward  as  inner  and  outer  tubules.  The  single 
median  tail  vessel  ends  blindly  near  the  posterior  end  of  the  tail;  it  sometimes 
receives  tributaries,  but  this  is  not  always  the  case. 

The  bladder  is  a  median  posterior  structure  opening  to  the  exterior  thru 
the  dorsal  pore.  It  is  usually  muscular,  unpaired.  It  v^aries  greatly  as  to 
size  and  shape.  It  may  be  p3Tiform  (Fig.  90),  obo\^te  (Fig.  93),  crenate 
(Figs.  55,  81),  truncate  or  obtnmcate  (Figs.  60,  100),  falciform  (Looss,  1896, 
Fig.  146),  or  lunar  (Looss,  1896,  Fig.  179). 

The  physiological  and  morphological  bladders  are  not  always  the  same. 
The  former  may  encroach  on  the  lateral  tubules  in  order  to  increase  its  capa- 
city. This  may  consist  of  mere  enlargements  of  the  cornua  without  any  change 
in  structure  (C  glandidosa,  Fig.  60;  C  micropharynx,  Fig.  90).    On  the  other 


391  LIFE  HISTORY  OF  TREMA  TODES—FA  UST  39 

hand  the  needs  for  a  muscular  enlargement  sometimes  cause  the  musculariza- 
tion  of  the  cornua  (C.  dendritica,  Fig.  81;  C.  crenata,  Fig.  55;  and  C.  racemosa, 
Fig.  100).  In  C.  diaphana  (Fig.  76)  the  modification  of  structure  has  taken 
place  before  the  enlargement  of  the  long  median  vessel  and  the  lateral  tubes. 

The  capillaries  tributary  to  the  lateral  tubules  are  represented  in  their 
most  simple  form  in  C.  micropharynx.  The  internal  anterior  vessel  may 
move  forward,  as  in  C.  crenata,  or  become  rudimentary,  as  in  C.  glandulosa. 
The  external  anterior  tubule  is  usually  the  most  fully  developed. 

It  is  important  to  note  that  the  lateral  systems  of  the  xiphidiocercariae 
never  anastomose  or  coalesce  in  any  way.  Thus  the  median  sagittal  plane 
acts  as  a  "watershed." 

In  the  forms  studied  no  large  flame  cells  were  found  in  the  course  of  the  ex- 
cretory system.  If  any  minute  flame  cells  were  present  they  were  concealed 
by  the  thick  integument. 

The  literature  shows  a  paucity  of  observations  on  the  flame  cells  of  larval 
and  adult  distomes.  Ssinitzin  (1905)  shows  the  details  of  the  flame  cells 
in  Gorgordera  pagenstecheri  and  in  Phyllodisiomum  folium.  They  consist  of  an 
ameboid  cytoplasm  in  which  is  imbedded  a  spheroid  nucleus  with  rich  chro- 
matic inclusions.  This  cell  is  the  terminus  of  the  capillary  (cl).  It  is  ordi- 
narily funnel-shaped,  but  when  distended  becomes  deeply  reniform.  The 
junction  of  the  flame  cell  and  the  capillary  is  marked  by  a  considerable  number 
of  cilia  which  vibrate  rythmically,  giving  rise  to  Ssinitzin 's  characterization, 
"vibratile  tip  cell  of  the  excretory  system." 

A  detailed  study  of  the  flame  cell  of  the  adult  distome  is  given  by  Looss 
(1896:110;  Figs.  72,  77)  for  Distomum  sanguineutn  Sons.  The  details  of  the 
cell  per  se  are  not  appreciably  different  from  those  given  by  Ssinitzin,  but 
the  distribution  of  the  flame  cells  thru  the  body  of  the  distome  is  described. 
There  are  four  symmetrically  paired  groups  of  three  cells  each  in  the  middle 
of  the  body,  and  one  pair  of  two  cells  each  in  the  anterior  and  posterior  reaches 
of  the  body,  making  sixteen  pairs  of  flame  cells  and  capillaries  in  all  (Fig.  77). 
This  probably  gives  an  indication  of  the  arrangement  of  the  flame  cells  in  the 
typical  distome.  In  Distomum  isoporum  (Looss,  1894,  Fig.  103)  six  paired 
groups  of  ultimate  tubules  are  figured  with  four  flame  cells  to  each  group, 
making  forty-eight  flame  cells  in  all.  In  Distomum  cylindraceum  (Fig.  163) 
there  are  six  paired  groups  of  capillaries  with  three  flame  cells  to  each  group, 
totalling  thirty-six  flame  cells.  Thus  the  number  of  flame  cells  is  not  constant 
in  different  species  but  ordinarily  remains  constant  for  each  species. 

Looss  (1894:249,  250;  Fig.  186)  suggests  that  the  fundamental  larval  system 
is  the  fundamental  system  of  the  adult.  Extension  and  modification  occur 
thru  a  dichotomy  of  the  existing  capillaries  and  flame  cells,  and  an  encroach- 
ment of  the  tubules  upon  the  capillaries.  The  greatest  modification  takes 
place  during  encystment,  altho  this  is  in  no  sense  a  metamorphosis. 

Among  adult  American  distomes  the  excretory  system  of  Microphallus 
opacus  Ward  alone  has  been  worked  out  with  the  exactitude  of  the  Euro- 
pean workers  (Wright,  1912,  PL  17,  Figs.  1,  2).    This  form  has  the  distome 


40  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [40 

Y-shaped  bladder  and  cornua.  There  are  only  eight  paired  capillaries, 
and  only  sixteen  flame  cells.  This  condition  constitutes  a  reduction  of  flame 
cells  from  the  average  types,  a  reduction  which  can  not  be  entirely  accounted 
for  by  the  small  size  of  the  species. 

2.  The  Echinostome  type.  This  family  of  distomes  is  characterized  by 
simplicity  of  detail  in  the  excretory  system  except  at  the  head  of  the  main 
lateral  vessel.  The  bladder  is  not  markedly  muscular.  The  pair  of  lateral 
vessels  arise  from  the  anterior  median  region  of  the  bladder,  and  not  from  the 
horns  of  this  vesicle  as  in  the  xiphidiocercariae.  The  main  trunks  do  not 
divide  but  proceed  to  the  cephalic  extremity  along  the  lateral  margins.  They 
sometimes  receive  small  tributaries  along  their  course.  In  the  cephalic  region 
the  vessel  commonly  flexes  back  on  itself.  Such  flexure  may  continue  back  to 
the  posterior  extremity  of  the  body,  as  in  C  reflexae  (Cort,  1915,  Fig.  43),  or 
may  continue  caudad  only  a  short  distance,  reflexing  a  second  time  (C.  biflexa, 
Fig.  135).  An  intermediate  form,  C.  echinata,  has  been  described  by  Looss 
(1894:191),  where  the  first  flexure  continues  caudad  while  another  part  is 
reflexed  cephalad. 

A  modification  of  the  type  represented  by  C.  biflexa,  where  the  double 
flexure  is  entirely  within  the  cephalic  region,  is  seen  in  C.  trisolenata  (Fig.  109). 
Either  the  end  of  the  flexure  has  been  fused  to  the  most  anterior  part  of  the 
main  vessel,  or  the  middle  portion  of  the  system  has  been  modified.  As  a 
result  a  triangular  channel  system  has  been  formed  at  the  anterior  end  of  this 
excretory  system. 

The  characteristic  feature  of  the  excretory  system  in  the  two  species  of 
echinostomes  is  the  triplet  of  flame  cells  at  the  anterior  part  of  the  system. 
A  detailed  study  of  the  flame  cells  in  C.  biflexa  is  found  in  figure  138.  The  cells 
are  situated  in  the  pockets  communicating  with  the  ultimate  part  of  the  re- 
flexed  tubule.  Cell  a  is  found  in  the  sinus  between  the  secondary  and  tertiary 
vessel.  It  points  upward  and  outward.  It  is  the  smallest  of  the  three  cells. 
Cell  c  occupies  the  swollen  end  of  the  tertiary  vessel.  It  is  the  largest  of  the 
three  vessels;  its  ciUa  are  the  most  rythmical  of  the  group.  Cell  b  Hes  midway 
between  cells  a  and  c.  It  points  downward  and  inward.  Cells  a  and  b  func- 
tion in  bringing  the  excretory  wastes  into  the  vessel  from  the  surrounding 
tissue  and  cell  c  directs  the  excretory  material  along  the  vessel. 

The  excretory  system  of  certain  species  of  echinostome  cercariae  contain 
granules.  These  granules  have  been  found  in  all  C.  trisolenata  examined; 
they  are  found  in  the  lateral  vessels  from  the  region  of  the  pharynx  posteriad 
to  the  acetabulum.    They  have  not  been  seen  in  C.  biflexa. 

The  excretory  system  in  the  tail  of  echinostome  cercariae  is  not  uniform. 
In  C.  trisolenata  there  is  a  single  median  tube  with  no  prominent  tributaries. 
In  C.  biflexa  a  median  tube  runs  two-fifths  the  distance  posteriad,  where  it 
divides  to  form  two  tubules  which  proceed  distad.  In  C.  trivohis  and  C. 
reflexae  (Cort,  1915,  Figs.  39,  43)  the  median  vessel  of  the  tail  courses  back- 
ward about  one-fifth  way  and  ends  there  in  a  bifurcation,  the  ends  of  which 


41]  LIFE  HISTORY  OF  TREMATODES— FAUST  41 

open  to  the  sides.  The  hiflexa  type  seems  to  be  intermediate  between  the 
echinostome  type  described  by  Cort  and  the  more  common  distome  type.  It 
is  highly  probable  that  the  excretory  system  of  the  echinostome,  with  three 
flame  cells  in  the  anterior  portion  of  the  system  and  possibly  several  smaller 
ones  further  caudad,  has  arisen  from  the  primitive  distome  type.  In  most 
cases,  the  posterior  flame  cells  have  become  fused  into  larger  ones,  so  that  only 
three  flame  cells  remain  in  the  anterior  part  of  the  system  in  C.  trisolenata  and 
C.   biflexa. 

3.  The  Furcocercaria  type.  The  mature  apharyngeal  distome  cercaria 
of  the  furcocercous  type  (i.e.  schistosome)  has  a  very  small  bladder  in  the 
posterior  part  of  the  body  and  two  lateral  vessels  running  cephalad.  The 
unpaired  portion  of  the  tail  has  a  single  median  canal,  which  is  united  to  the 
system  of  the  trunk  thru  an  "eyelet  anastomosis."  The  median  tubule  of 
the  tail  forks  to  enter  the  rami.  The  origin  of  the  caudal  vessels  has  been 
worked  out  by  Looss  (1896,  Figs.  172-174)  for  C.  vivax  Sonsino.  These  tubules 
arise  as  the  posterior  extension  of  the  paired  body  excretory  tubes.  Their 
fusion  in  the  common  portion  of  the  tail  occurs  after  the  rami  have  become 
well  differentiated.  The  "eyelet"  is  an  index  of  the  original  paired  system 
in  both  body  and  tail. 

A  study  of  the  species  C  gracillima  (Fig.  143)  and  C.  tuberistoma  (Fig.  155) 
shows  the  main  features  of  the  vivax  type.  The  small  bladder,  the  lateral 
canals,  the  median  caudal  tube,  bifurcating  distally  to  proceed  into  the  rami, 
the  "eyelet"  at  the  junction  of  the  body  and  the  tail — all  of  these  seem  to  be 
constant  for  the  entire  group.  Beyond  these  characters  the  features  of  the 
several    species    are    divergent. 

In  C.  gracillima  (Figs.  143,  145)  the  caudal  portion  is  extremely  simple, 
containing  only  the  common  median  tubule  and  the  forked  tubule  system 
entering  the  rami.  Unlike  C.  vivax  with  its  three  pairs  of  flame  cilia  in  the 
common  caudal  tubule,  this  species  has  no  flame  cells  in  the  caudal  portion 
of  the  worm.  The  system  in  the  body  of  the  cercaria  has  a  non-muscular 
trilateral  bladder,  small  posterior  tubes  arising  from  the  lateral  tubes,  and 
a  ciliary  pocket  about  one-fourth  way  from  the  posterior  margin  of  the  body,  on 
the  inner  wall  of  each  lateral  tube  (Fig.  145).  At  the  posterior  margin  of 
this  ciliary  pocket  small  tributary  canals  from  the  median  plane  flow  into  the 
main  canal.  Slightly  cephalad  is  another  pocket,  somewhat  larger  than  the 
ciliary  pocket,  filled  with  small  granules  of  various  sizes  and  shapes.  Into 
this  pocket  four  or  five  small  canals  empty,  the  median  ones  of  which  anstomose 
with  their  mates  from  the  opposite  side.  No  ciliary  cells  have  been  found  in 
the  terminations  of  the  capillaries. 

In  C.  tuberistoma  the  caudal  portion  of  the  worm  is  characterized  by  five 
transverse  canals.  Another  pair,  anterior  to  these,  is  conspicuous  because 
it  runs  forward  for  a  short  distance  and  is  then  reflexed  backward  for  some 
distance  (Fig.  155).  The  eyelet  and  the  bladder  are  both  muscular.  In  the 
body  portion  there  are  no  pockets  for  the  lodgement  of  granules  and  no 
transverse  anastomoses.    No  flame  cells  have  been  found  in  this  larva. 


42  ILLINOIS  BIOLOGICAL  MONOGRAPHS  f42 

A  comparison  of  the  furcocercous  larvae  with  the  Schistosomatidae  shows 
the  striking  similarity  of  the  excretory  systems  of  these  forms.  Looss  (1895) 
finds  the  system  of  male  and  female  Schistosoma  haematobium  alike,  altho 
that  of  the  female  may  be  sUghtly  better  developed,  due  to  a  minimization 
of  the  musculature.  The  bladder  is  median,  non-muscular,  except  for  a 
weak  sphincter  at  the  pore.  It  receives  the  two  longitudinals  at  its  antero- 
lateral reaches.  There  is  no  median  canal  (p.  72).  Many  of  the  laterals  are 
dendritic,  altho  they  do  not  anastomose.  Small  flame  ciMa  are  at  the  heads 
of  the  capillary  tubes  of  Sn  to  4/1  diameter.  These  flame  cells  and  capil- 
laries are  intra-cellular,  and  not  surrounded  by  an  epithelial  lining. 

D.  Excretory  system  of  the  Parthenitae.  Details  are  given  only  in  ob- 
servations of  Looss  (1892:158-161)  for  the  excretory  system  of  young  parthe- 
nitae. The  "protonephridia"  of  Ssinitzin  (1911:77-80;  PI.  1,  Figs.  24,  25), 
described  by  him  in  connection  with  the  birthpore  of  the  redia,  have  not  been 
proved  to  have  an  excretory  function. 

According  to  Looss  the  excretory  sytem  both  in  the  sporocyst  and  redia 
arises  as  a  paired  structure,  from  which  capillaries  and  flame  cells  soon  arise. 
The  observations  of  the  writer  have  been  confined  to  the  adult  sporocyst  and 
redia  of  the  species  studied,  in  which  the  system  is  strikingly  different  from 
the  embryonic  condition.  In  many  cases  the  excretory  system  consists 
of  a  diamond  pattern  of  intercellular  channels,  without  any  clue  to  the  former 
bilateral  symmetry.  The  same  amount  of  modification  holds  for  both  sporo- 
cyst and  redia.  Even  in  the  holostome  redia  (Fig.  42)  this  diamond  pattern 
is  found.  No  flame  cells  have  been  found  in  adult  parthenitae.  This  distinct 
modification  of  the  excretory  system  in  parthenitae  is  not  surprising  in  view 
of  the  extraordinary  degeneration  of  the  animal  that  has  resulted  from  its 
endoparasitic  habits  during  its  entire  life. 

Excretory  granules.  The  excretory  granules  of  the  cercaria  and  parthenita 
are  spheroidal  and  have  the  general  appearance  of  glass  beads.  Their  re- 
fractive index  is  very  high.  The  size  of  the  concretions  is  variable  in  different 
groups  and  even  in  the  same  individual.  As  a  rule  the  granules  are  largest 
in  the  monostomes  and  holostomes. 

Few  writers  have  given  consideration  to  these  excretory  granules.  Thomas 
(1883:117)  says  for  Fasciola  hepatica  larvae  that  "the  yellowish  granules.  .  . 
appear  to  be  excretory  products  formed  within  the  cells  of  the  sporocyst  and 
then  ejected.  They  are  partially  soluble  in  acids,  leaving  an  organic  basis. " 
Looss  refers  to  them  as  opaque  concrement-granules  which  on  first  sight  throw 
the  boundaries  of  the  tubules  into  black  rehef  (1894:165).  They  are  insoluble 
in  alcohol  and  color  beautifully  in  stained  mounts.  Reference  is  made  to 
these  granules  by  Cort  (1915:16)  to  the  effect  that  the  tubules  of  the  mono- 
stomes are  filled  thruout  their  entire  length  "with  small  round  concretions 
which  disappear  in  the  process  of  preservation."  The  writer  has  found  that 
these  granules  are  not  usually  preserved  in  the  corrosive-acetic  fixing  fluids. 
However,  if  fixation  is  done  without  the  acid  fraction  of  the  fluid  the  granules 


43]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  43 

are  preserved.  Application  of  strong  acid  to  the  granule  causes  an  evolution 
of  gas.  The  granules  are  negative  to  inorganic  CO2  tests,  and  are  non-crystal- 
line, as  determined  by  the  petrographic  microscope.  They  take  hematoxylin 
stains  readily,  altho  they  do  not  stain  deeply.  They  give  no  Molisch  reaction. 
The  xanthroproteic  test  is  positive,  indicating  a  benzene  nucleus.  It  is 
probable  that  they  consist  of  a  conjugate  protein  before  fixation.  Fixation 
with  mercuric  chlorid  alters  them,  since  they  are  then  acid  and  alkali  re- 
sistent. 

Generalizations  on  the  excretory  sytem.  The  excretory  system  of  the 
trematodes,  including  both  cercariae  and  parthenitae,  is  essentially  a  bilateral 
system.  It  arises  as  two  paired  tubules,  which  fuse  in  the  bladder  region  of 
the  cercaria  to  form  the  vesicle.  The  mature  system  of  the  parthenitae  is 
highly  modified  from  the  primitive  type.  The  system  as  found  in  the  cer- 
caria is  carried  into  the  adult  without  very  profound  modification. 

Most  individuals  of  all  generations  contain  within  their  excretory  systems 
spheroidal  concretions,  which  are  waste  organic  products,  quite  probably 
derived  proteins.  They  lodge  in  the  main  tubes  and  are  expelled  thru  the 
excretory  pore. 

DIGESTIVE  SYSTEM 

The  most  uniform  system  in  the  Digenea  is  the  digestive  tract.  With  the 
exception  of  the  sub-order  Gasterostomata  and  the  super-family  Prostomata, 
the  enteric  canal  is  triclad  in  character.  The  main  features  of  difference  in 
the  various  families  of  the  group  is  the  modification  of  the  esophagus  region  of 
the  gut.  In  most  forms  there  is  a  pharynx  sphincter  just  within  the  oral 
pocket.  In  other  species  the  pharynx  is  small  and  inconspicuous.  In  still 
others  there  is  no  bulbus  around  the  esophagus,  but  in  its  stead  a  group  of 
gland  cells. 

The  digestive  system  in  the  cercaria  is  not  distinctly  a  larval  system  but 
practically  a  fully  matured  system.  In  some  cases  it  is  not  functional,  as  in 
the  Monostomata,  where  the  paired  ceca  are  still  filled  with  a  jell  (Fig.  13) ; 
in  the  Schistosomatidae  there  is  the  interesting  phenomenon  of  short  ceca  in 
some  species  {Cercaria  gracilUma)  and  entire  absence  in  others  (C  tuheristoma) . 
While  the  larval  digestive  glands  of  the  cercaria  may  not  be  retained  or  may  be 
metamorphosed  in  the  mature  worm,  nevertheless  they  are  functional  in 
most  larvae. 

The  forking  of  the  ceca  is  not  constant,  varying  in  different  species.  Even 
the  relative  length  of  the  parts  of  the  tract  varies  greatly  in  the  same  individual 
at  different  times,  due  to  the  extreme  limits  of  contraction  and  expansion  of 
the  larva,  so  that  this  relation  of  parts  can  not  be  entirely  depended  on  as  a 
basis  for  diagnosis.  As  a  whole  the  digestive  tract  is  remarkably  uniform  and 
simple,  which  might  be  expected  in  a  larva  in  which  the  food  supply  is  so 
accessible. 

The  sporocyst  has  no  digestive  tract,  but  takes  its  nourishment  directly 
thru  the  body  wall.  In  consequence  the  cells  of  the  epidermis  are  thin  and 
at  times  apparently  glandular,  as  in  the  stylet  cercariae. 


44  ILLINIOS  BIOLOGICAL  MONOGRAPHS  [44 

The  redia  has  a  gut-pouch  for  a  digestive  system,  with  a  pharynx  sphincter 
around  the  anterior  end.  Hence  the  epidermis  is  not  used  in  the  capacity 
of  food  transference,  and  is  heavily  Kned  beneath  with  an  integvmientary 
secretion.  For  securing  food  the  redia  of  Cercaria  pdlticida  is  provided  with 
an  oral  piercing  organ.  The  redia  of  C.  flabelliformis  is  equipped  with  paired 
mucin-salivary  glands. 

GENITAL  SYSTEM 

This  system  of  organs  has  been  the  most  constant  basis  of  classification 
of  adult  trematodes.  It  is  also  the  best  specific  criterion  for  the  larvae,  altho 
a  more  deUcate  technic  is  required  for  differentiation  of  the  genital  organs  in  the 
cercaria  than  in  the  adult  worm.  Because  these  organs  have  failed  to  come 
out  in  the  ordinar>^  preparations,  no  attempts  have  been  made  to  use  them  as 
basis  for  correlating  larvae  and  adults.  Cell  masses  have  been  figured  by  Looss 
(1896),  Ssinitzin  (1905,  1911)  Miyairi  and  Suzuki  (1914)  and  Cort  (1915),  but 
these  workers  have  not  in  any  case  showTi  them  in  detail.  By  means  of  a 
lengthy  staining  in  a  weak  solution  of  Delafield's  hematoxylin,  followed  by 
rapid  differentiation  and  then  neutralization  with  potassium  acetate  solutions 
in  the  higher  alcohols,  the  genital  organs  of  the  cercariae  have  been  traced 
with  a  degree  of  detail  not  previously  attained.  These  organs  have  been  found 
to  offer  valuable  data  for  correlating  cercariae  and  adult  trematodes. 

A.  Monostomata.  All  three  species  of  monostomes  on  which  observations 
have  been  made,  Cercaria  pellucida,  C.  kanadensis,  and  C.  urbanensis  Cort  are 
characterized  by  the  symmetrically  arranged  testes,  the  presence  of  Laurer's 
canal,  the  location  of  the  vitelline  glands  in  a  double  series  on  each  side  of  the 
body,  and  the  courses  of  the  uterus  and  vas  deferens.  Ssinitzin  (1905,  Fig. 
76)  shows  the  inner  series  of  five  paired  vitellaria  for  C.  ephemera  Nitzsch,  but 
he  has  figured  no  outer  series  of  three  glands,  such  as  are  found  in  the  three 
species  worked  out  by  the  \NTiter.  He  is  in  error  in  considering  them  cj'sto- 
genous  glands,  because  their  connection  is  traceable  thru  filiform  ducts  to  the 
ootype.  All  these  species  are  provisionally  referred  to  the  Notocotyhdae. 
With  the  growth  of  the  cercaria  to  the  adult  monostome  the  originally  distinct 
and  readily  recognizable  vitelline  elements  becomed  fused  in  part.  Looss 's 
figure  (1896,  Fig.  94)  of  Notocotyle  verrticosa  (Froel.)  shows  five  rather  poorly 
defined  foci  of  vitelline  elements  in  each  of  the  lateral  series.  It  is  possible 
that  the  five  inner  elements  of  the  series  have  become  fused  to  the  three  outer 
elements  of  the  series,  thus  causing  the  indefinite  outline  of  the  elements  in 
the  adult  worm.  The  vitelline  glands  of  Notocotyle  quinqueseriale  are  ap- 
parently eight  to  the  side.  Here  the  three  glands  of  the  outer  series  may  have 
been  introduced  between  the  five  glands  of  the  inner  series  (Barker  and  Laugh- 
lin,  1911,  PI.  1,  Fig.  10).  A  symmetrical  pair  of  \dtelline  ducts,  between  the 
inner  and  outer  series  of  glands,  leads  to  the  ootype. 

The  cercariae  which  the  writer  has  studied  in  this  group  are  readily  dis- 
tinguished by  a  comparison  of  their  genital  systems. 


45]  LIFE  HISTORY  OF  TREMATODES— FAUST  45 

In  Cercaria  pellucida  the  well-developed  cirrus  pouch  and  the  poorly  de- 
veloped vagina  reach  the  confines  of  the  excretory  trunk  just  behind  the  median 
eye.  In  C.  konadensis  the  cirrus  pouch  and  the  vagina  are  both  equally  devel- 
oped. The  former  is  falciform,  the  later  pyriform.  The  vagina  is  lateral 
to  the  cirrus  pouch  but  is  somewhat  posterior  to  it.  The  genital  pore  in 
C.  pellucida  is  not  as  far  posterior  as  that  in  C.  konadensis.  In  this  species, 
as  well  in  C.  urhanensis,  the  testes  are  marked  by  definite  cell  masses,  while 
in  C.  konadensis  the  testicular  masses  are  much  more  indefinite.  They  are 
small  in  each  case  and  lie  ventral  to  the  vitelline  organs.  The  course  of  the 
vasa  efferentia  is  clearly  outlined. 

On  the  basis  of  the  structure  of  the  vitellaria  alone  these  species  can  be 
differentiated  in  the  cercaria  stage.  In  C.  pellucida  the  glands  are  actually 
spiculate  in  outline,  flattened  dorsoventrally.  The  vitelline  material  is 
finely  granular  and  closely  massed.  In  C.  konadensis  the  glands  are  decidedly 
dendritic,  and  the  granules  are  diffuse.  In  C.  urhanensis  the  glands  are  lobate 
and  the  fine  granules  are  included  within  a  dense  mucoid  matrix. 

B.  Holostomata.  The  genitalia  of  the  Holostomidae  and  Hemistomidae 
will  be  considered  separately. 

1.  Holostomidae.  The  thickness  of  the  tetracotyle  larva,  together  with 
the  thickness  of  the  cysts,  in  which  the  majority  of  these  individuals  have  been 
found,  has  prevented  a  study  of  the  genital  system  from  stained  toto  mounts. 
However,  these  organs  come  out  clearly  in  frontal  sections  of  7/i  thickness 
(Fig.  39).  In  Cercaria  flabelliformis  the  ovary  is  situated  just  caudal  to  the 
posteriormost  muscular  lappet.  A  short  oviduct  proceeds  dorsad  to  the 
ootype.  The  uterus  winds  posteriad  to  the  genital  pouch.  The  vitelline 
glands  are  long  paired  cords.  In  C.  flabelliformis  they  are  composed  of  large 
vesicular  glands  (Fig.  39) ;  in  Tetracotyle  pipientis  (Fig.  47)  they  are  loosely 
follicular.  The  testes  are  paired  structures  which  may  occupy  positions  from 
the  plane  of  the  ovary  (T.  pipientis)  to  the  plane  of  the  genital  pouch  (C. 
flabelliformis).  The  pouch  is  muscular  and  opens  posteriad,  ventral  to  the 
excretory  pore. 

Thus  these  genital  organs  are  tj^ically  holostome  in  character,  correspond- 
ing to  the  main  features  described  for  the  adults  by  Brandes  (1891),  Thoss 
(1897),  and  Johnston  (1904).  They  are  sufficiently  detailed  in  this  stage  of 
the  species  development  to  be  of  diagnostic  value. 

2.  Hemistomidae.  In  this  family  all  of  the  genital  organs  are  situated 
entirely  posterior  to  the  acetabulum.  The  primitive  genital  pore,  anterior 
to  the  acetabulum,  has  lost  its  connection  with  the  genitalia,  and  with  the 
addition  of  muscular  elements  has  assumed  a  suctorial  function. 

The  species  Cercaria  ptychocheilus  has  an  ovary  elongate  in  a  transverse 
plane,  nearly  spatulate,  situated  just  behind  the  acetabulum.  It  is  granulate, 
compact,  and  stains  deeply  with  hematoxylin  dyes.  At  its  left  it  merges 
into  the  oviduct,  a  large  coiled  tubule,  which  bends  on  itself  three  times  just 
behind  the  margin  of  the  ovary,  then  empties  into  the  ootype  just  anterior 


46  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [46 

to  the  bursa  copulatrix.  The  densely  massed  cells  of  the  glands  in  the  vicinity 
of  the  ootype  lie  just  above  this  organ.  The  testes  are  situated  at  the  right 
side  just  ventral  to  the  ovary.  They  are  small  compact  glands,  and  have  no 
ducts  at  this  stage  of  development.  The  vitelline  ducts  from  the  diffuse 
vitelline  follicles  meet  the  other  genital  products  in  the  ootype.  The  genital 
bursa  is  very  large  and  muscular,  and  hes  just  ventral  to  the  excretory  bladder. 
Symmetrically  arranged  glands,  with  glandular  nuclei  and  hyaUne  cytoplasm, 
empty  into  it  from  the  postero-lateral  reaches.  They  vary  in  number  from 
seven  to  ten  on  each  side. 

With  the  exception  of  these  glands  emptying  into  the  bursa,  all  of  the  genital 
organs  of  this  larva  lie  in  the  anterior  patelliform  region.  With  the  exception 
of  the  later  formation  of  a  uterine  duct  between  the  oot}^e  and  the  bursa,  all 
of  the  organs  are  in  the  approximate  location  where  they  wUl  be  in  the  adult 
worm.  The  massing  of  the  organs  in  the  anterior  portion  of  the  animal  is 
undoubtedly  correlated  with  the  abbreviation  of  the  appendicular  portion  of 
the  species. 

The  literature  on  larval  hemistomes  (Diplostomulum)  shows  that  von 
Nordmann  (1832:34-35,  PL  III,  Fig.  1)  has  described  an  egg  pouch  for  D. 
volvens  and  two  symmetrically  arranged  testes,  with  ducts,  in  the  region  of 
the  acetabulum.  Leidy  (1904:111)  describing  D.  grande  (Diesing),  speaks  of 
"ovaries,  dusky  yellow."  Since  the  ovary  in  the  Holostomata  is  single,  the 
organs  thus  described  are  possibly  testes. 

The  bursa  is  the  muscular  organ  par  excellence  in  Cercaria  ptychocheilus. 
Muscle  elements  protrude  into  the  atriiun,  so  that  a  constriction  exists  between 
the  anterior  and  posterior  portions  of  the  organ. 

The  genital  systems  of  the  holostome  and  the  hemistome  are  similar  in 
those  features  in  which  they  differ  from  the  distomes.  They  have  modified 
their  primitive  genital  pore  so  that  it  has  either  become  rudimentary  or  has  as- 
sumed a  muscular  function.  The  sperm  ducts  and  the  uterine  duct  empty 
into  the  pouch  at  the  posterior  end  of  the  animal,  instead  of  the  atrium  an- 
terior to  the  acetabulum.  The  new  genital  p)ore  is  posterior  to  the  ootype, 
and  ventral  to  the  excretory  pore. 

C.  Distomata.  The  genital  organs  of  the  distomes  are  different  in  various 
families. 

1.  Xiphidiocercariae.  The  genital  organs  in  these  cercariae  are  readily 
defined  with  reference  to  the  acetabulum.  They  are  mostly  situated  in  the 
middle  of  the  ventral  side  of  the  larva  just  behind  the  acetabulum  or  shghtly 
posterior  to  this  position.  The  ootype  is  posterior  and  dorsal  to  the  acetabulum. 
The  uterus  coils  around  the  right  side  of  the  acetabulimi.  It  ends  in  a  blimt 
or  tapering  ceU  mass.  Laurer's  canal  is  on  the  left  of  the  median  line,  just 
behind  the  middle  of  the  acetabulum.  It  is  present  in  all  of  the  species  of 
stylet  cercariae  examined.  Only  in  two  species  are  the  testicular  cell  masses 
outlined.    In  C.  crenata  (Fig.  59)  these  glands  consist  of  two  large  ovate  masses. 


47]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  47 

In  C.  dendritica  (Fig.  86)  the  testes  are  small,  situated  closely  behind  the  oo- 
type.  In  no  case  is  the  ovary  clearly  differentiated  from  the  region  of  the 
00  type. 

The  vitellaria  are  definitely  outlined.  These  glands  in  C.  glandulosa 
(Fig.  66),  C.  diaphana  (Fig.  78),  and  C.  micro  pharynx  (Fig.  96)  are  much  more 
alike  than  those  in  the  remainder  of  the  stylet  species.  The  vitelline  follicles 
of  C.  dendritica  (Fig.  86),  and  C.  crenata  (Fig.  59)  are  noticeably  dissimilar, 
having  on  the  one  hand,  a  system  extending  the  entire  length  of  the  body, 
and,  on  the  other  hand,  a  system  confined  to  the  immediate  vicinity  of  the 
ootype. 

The  genital  organs  and  ducts  of  C.  racemosa,  the  lateral  fin  type  (Fig.  104), 
bear  some  resemblance  to  those  of  C.  dendritica  (Fig.  86).  However,  Laurer's 
canal  is  very  prominent  in  this  fintail  species,  while  in  C.  dendritica  it  is  not 
so  prominent.  Instead  of  coiUng  around  the  right  side  of  the  acetabulum, 
the  uterus  in  C.  racemosa  makes  four  double  obHque  coils  dorsal  to  the  acetabu- 
lum. The  ovarian  cell  mass  is  dorsal  to  the  ootype  and  connects  with  that 
organ  thru  a  short  duct.    The  testes  masses  have  not  been  observed. 

2.  Echinostomidae.  The  two  species  of  this  group  which  have  been 
studied,  C.  trisolenata  and  C.  hiflexa,  vary  in  the  structure  of  their  genital 
organs  most  markedly.  In  view  of  this  diversity  it  does  not  seem  advisable 
to   take   them  up  in  detail  in  this  comparative  phase  of  the  study. 

3.  Furcocercariae.  The  material  of  Cercaria  gracillima  was  studied  with 
especial  reference  to  the  genital  cell  masses,  both  in  the  totos  and  the  section 
mounts.  The  main  system  consists  of  the  ovary-uterus  mass  on  the  right 
and  the  cirrus  mass  on  the  left,  both  in  the  vicinity  of  the  acetabulum.  The 
vitellaria  are  lateral  and  empty  into  the  ootype  thru  transverse  ducts  (Fig.  149). 
The  testicular  follicles  are  numerous,  24  or  25  having  been  counted.  They 
are  proUferated  from  a  posterior  germ  mass,  which  is  ventral  to  the  bladder 

NERVOUS  SYSTEM 

One  of  the  earlier  and  better  known  system  of  the  adult  trematode  was 
the  nervous  system.  Leuckart  (1863:462)  states  that  Bojanus  and  Mehlis 
were  famihar  with  the  gross  anatomy  of  the  nervous  system  of  the  larger  flukes, 
and  that  von  Laurer,  Diesing  and  Siebold  as  well  as  the  elder  van  Beneden 
were  acquainted  with  the  nervous  systems  of  both  large  and  small  worms. 
Leuckart  described  the  sy tem  for  Fasciola  hepatica  and  Dicrocoelium  lanceatum-. 
He  states  that  there  are  two  or  three  stems,  the  anterior  dorsalis  and  an- 
terior lateralis  and  the  thick  posterior  ven trails.  Somewhat  later  Lang  (1880: 
46-50),  substantiates  the  work  of  Leuckart  and,  in  addition  describes  the  dor- 
sal posterior  and  acetabular  innervation.  Gaffron  (1884)  and  Looss  (1892, 
1894,  1895)  have  placed  the  nerve  anatomy  of  the  adult  trematode  on  a 
firm  foundation.  Hofmann  (1899),  Wright  (1912),  and  Monticelli  (1914)  have 
confirmed  the  work  of  earlier  workers.  Nor  has  the  finer  work  on  the  nerve 
endings  and  the  ganglion  cells  been  overlooked.    Many  of  the  earlier  writers 


48  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [48 

made  out  the  ganglion  cells  of  the  pharynx  region  and  recorded  their  ob- 
servations on  the  nuclei.  Bettendorf  (1897),  working  on  Fasciola  hepatica 
with  intra  vitam  methylene  blue  and  Golgi  methods,  has  brought  out  clearly 
and  convincingly  the  nervous  sytem  of  this  worm.  This  study  has  been  aug- 
mented by  the  work  of  Zailer  (1914). 

In  view  of  the  extensive  study  of  the  nervous  system  of  the  adult  tre- 
matode,  it  is  a  matter  of  no  Httle  surprise  that  so  Uttle  has  been  done  on  the 
nervous  structure  of  the  cercaria  and  the  parthenita.  Looss  (1894:245)  has 
confessed  the  difficulty  in  making  such  a  study  and  had  observed  that  "ein, 
wie  es  scheint,  nicht  unbetrachtUcher  Theil  derselben  fallt  in  die  Zeit  der 
Cercarienentwicklimg,  imd  weiterhin,  ist  auch  der  ganze  Apparat  wahrend 
seiner  AusbUdungzeit,  dass  es  mitimter  recht  schwer  ist,  zu  entscheiden  was 
zu  ihm  und  was  zu  dem  umgebenden  Parenchyme  gehort. "  However,  Looss 
depended  on  Hving  mounts  for  his  study  and  did  not  use  preserved  material 
or  avail  himseh"  of  intra  vitam  methylene  blue  technic.  By  the  use  of  an 
eosin  coimterstain  against  a  hematoxyhn  background  the  writer  has  been 
able  to  secure  remarkably  clear  sections  showing  with  extraordinary  deUcacy 
the  nerve  branches  as  well  as  the  central  nervous  system.  It  is  the  purpose 
of  this  section  of  trematode  morphology  to  present  data  and  observations 
on  the  development  and  structure  of  the  nervous  system  in  parthenita  and 
cercaria. 

The  central  nervous  system  of  the  adult  trematode  consists  of  two  central 
ganglion  masses,  situated  dorsal  and  lateral  to  the  pharynx  and  yoked  together 
by  a  transverse  commissure  passing  dorsal  to  the  pharynx.  The  appearance 
of  this  structure  has  been  aptly  described  by  Lang  (1880:46)  as  a  saddle 
between  oral  sucker  and  pharynx.  In  cross  section  it  is  lunar.  Here  are 
centered  the  most  of  the  gangUon  cells,  altho  they  are  frequently  found  poster- 
iorly, and  often  in  the  sensory  apparatus  of  the  oral  and  ventral  suckers.  The 
system  also  has  a  subesophageal  commissure  which  differs  in  size  and  shape  in 
different  species  of  flukes.  Extending  forward  into  the  region  of  the  oral 
sucker  are  three  pairs  of  nerve  trunks,  the  dorsalis,  lateraUs,  and  ventraHs. 
Of  these  three  the  latter  is  the  most  fully  developed.  It  has  a  ramus  muscular- 
is  which  is  both  motor  and  sensory  (Zailer),  and  an  extensive  connection  with 
the  oral  ner\'e  ring.  The  anterior  laterahs  is  also  a  strongly  developed  trunk, 
with  a  ramus  muscularis  and  a  ramus  palpaUs,  and  transverse  commissures 
to  the  anterior  dorsahs  and  posterior  lateralis.  The  anterior  dorsaUs  is  a 
weakly  developed  nerve  which  innervates  the  apical  sensory  field.  A  trans- 
verse commissure  connects  the  two  dorsales  above  the  head  muscle  sheath. 
In  addition  to  these  three  primary  trunks,  the  palatinus,  a  weak  motor  nerve, 
lies  internal  to  the  anterior  ventrahs.  Posterior  to  the  central  nervous  system 
are  the  three  posterior  trunks,  the  dorsahs,  laterahs,  and  ventrahs.  The  ven- 
tral trunk  is  by  far  the  most  strongly  developed.  In  addition  to  these  is  the 
small  but  conspicuous  internal  branch  of  the  ventrahs  known  as  the  pharyn- 
geahs.  It  occupies  a  posterior  position,  corresponding  to  the  palatinus  anter- 
ior to  the  central  nervous  system. 


49J  LIFE  HISTORY  OF  TREMATODES— FAUST  49 

Braun  (1893:683)  considers  the  ventralis,  dorsalis,  and  pharyngealis  to  be 
the  three  pairs  of  posterior  nerves.  However,  the  consistent  course  of  the 
lateralis  to  the  posterior  extremity  of  the  body,  its  early  appearance 
in  the  embryology  of  the  worm,  and  its  conmiissural  connections  with  the 
anterior  lateralis  and  posterior  dorsalis  surely  prove  its  right  to  a  place  in  the 
rank  of  the  primary  posterior  nerve  trunks. 

The  nervous  system  of  the  monostomes  has  been  worked  out  by  Jager- 
skiold  (1891)  for  Ogmogaster  plicatus  (Crepl.),  and  by  Monticelli  and  Looss 
for  Catatropis  verrucosa  (Frol.).  Looss  (1896:149)  considers  the  system  similar 
to  the  distome  type.  "Je  n'hesite  pas  a  attribuer  au  systeme  nerveux  de 
notre  ver  une  construction  analogue  a  celle  que  nous  avons  deja  signalee  chez 
un  bon  nombre  de  Trematodes  digeneses."  However,  Looss  (1896:11-16) 
was  not  able  to  make  out  clearly  the  anterior  trunks.  Jagerskiold  (1891 :14-16) 
describes  the  cerebral  ganglion  masses  with  the  transverse  commissure,  the 
posterior  ventralis,  dorsaUs,  and  lateralis,  and  the  three  anterior  trunks,  short 
and  thorn-like,  the  homologs  of  the  dorsalis,  lateralis,  and  ventralis.  A  stem, 
designated  as  the  "fourth,"  arising  from  the  anterior  reaches  of  the  cerebral 
masses,  passes  ventrad  to  the  region  below  the  oral  sucker;  it  seems  probable 
that  it  is  the  palatinus.  The  only  real  modification  from  the  distome  type 
is  the  absence  of  the  acetabular  innervation,  due  to  the  loss  of  this  organ. 

In  the  Amphistomata  adults  among  the  earlier  writers  Lejtenyi  (1881 :142- 
144),  working  on  Gastrodiscus  polymastos  Leuck!,  described  two  ganglion  centra 
with  the  dorsal  commissural  bridge,  but  with  only  one  anterior  and  one  poster- 
ior pair  of  trunks.  In  contrast  to  this  incomplete  description  is  that  given 
by  Looss  (1896:21,  22)  for  Gastrodiscus  aegyptiacus  (Cobb),  where  the  usual 
distome  nerve  trunks,  were  found,  and,  in  addition,  a  median  anterior  and  a 
median  posterior  nerve.  Looss  has  worked  out  the  nerve  anatomy  for  Am- 
phistomum  suhclavatum  Rud.  in  even  greater  detail  (1892:151;  Taf.  19, 
Figs.  1,  2,  ),  and  finds  that  they  correspond  to  the  distome  type,  except  for 
the  innervation  of  the  posterior  sucker. 

The  one  group  of  the  Digenea  where  the  nervous  system  has  been  almost 
entirely  neglected  is  the  Holostomata.  Brandes  (1891)  states  that  none  of 
the  workers  of  the  nervous  system  up  to  his  day  have  worked  on  the  holosto- 
mids.  He  has  observed  only  the  central  nerve  center  lying  above  the  posterior 
portion  of  the  pharynx,  an  anterior  and  a  posterior  pair  of  nerve  trunks,  the 
tracings  of  which  he  has  found  in  sections.  Thoss  (1897),  working  on  Holo- 
stotnum  cucullus,  finds  the  main  nerve  center  lying  dorsal  to  the  origin  of  the 
esophagus,  with  two  pairs  of  anterior  and  one  pair  of  posterior  nerve  trunks. 

The  central  nervous  system  of  Cercaria  trisolenata,  the  echinostome, 
consists  of  two  masses  of  ganglion  cells  and  the  dorsal  commissure  lying  con- 
cavely  on  the  dorsal  side  of  the  large  muscular  pharynx.  The  commissure  is 
broad  and  flat.  The  dorsal  surface  of  the  gangUon  masses  and  the  commissure 
present  a  smoothly  curved  surface,  but  on  the  ventral  side  the  ganglia  bulge 
out  against  the  pharynx.  The  anterior  trunks  consist  of  the  dorsalis,  lateralis, 
ventralis,  and  the  palatinus.    The  paired  dorsales  arise  together  with  the 


50  JLUNOIS  BIOLOGICAL  MONOGRAPHS  [SO 

laterales  and  proceed  forward  with  them  for  some  distance.  After  separation, 
the  dorsalis  runs  more  median,  then  flexes  outward  and  dorsalward  over  the 
oral  hood,  proceeding  toward  the  apical  sensory  center.  The  lateralis  at  the 
point  where  it  leaves  the  dorsalis  proceeds  outward  and  forward,  so  that  it 
reaches  a  level  slightly  below  the  plane  of  the  central  nervous  system.  SUghtly 
after  diverging  from  the  dorsaUs  the  lateralis  gives  back  a  commissure  to  the 
dorsalis.  This  dorsolateral  connective  fuses  with  the  dorsaUs  just  behind 
the  posteriormost  branching  of  this  trunk.  Arising  from  the  most  ventral 
reaches  of  the  gangUon  center  is  the  ventralis,  a  broad  flat  trimk,  which  courses 
outward  and  downward  to  the  oral  Hp  of  the  oral  sucker.  Internally  it  gives 
oflF  the  palatine,  which  Ues  just  lateral  to  the  pharynx. 

Caudal  to  the  central  nervous  system  arise  the  four  pairs  of  posterior 
trunks,  the  dorsales,  the  laterales,  the  ventrales,  and  the  pharyngeales.  The 
dorsaUs  branch  arises  dorsal  and  slightly  lateral  to  the  junction  of  the  gangHon 
and  the  commissure.  It  runs  straight  backward,  slightly  dorsal  to  the  plane 
of  the  central  nervous  system.  The  lateralis  arises  sUghtly  lateral  to  the 
dorsaUs;  its  path  Ues  outward  and  backward.  The  ventralis  arises  from 
the  very  heart  of  the  gangUon  mass.  It  spreads  outward  and  then  runs  back- 
ward paraUel  to  its  mate.  The  ventral  commissure,  arises  just  median  to  the 
origin  of  the  posterior  ventraUs  flexing  below  the  prepharyngeal  opening.  It 
is  stout  and  bowed  considerably  downward.  Between  the  commissure  and 
the  ventraUs  arises  the  pharyngeaUs. 

In  a  germ  ball  of  Cercaria  trisolenata  some  45^4  by  60ai  in  size,  the  central 
nervous  system  is  weU  developed.  This  may  be  called  the  butterfly  stage 
(Fig.  121).  At  this  period  there  are  two  pairs  of  main  tnmks  anterior  and 
four  pairs  posterior  to  the  central  gangUon  mass.  The  anterior  trunks  are 
the  ventrales  and  the  laterales.  By  reference  to  the  next  stage  in  the  devel- 
opment (Fig.  122),  the  dorsales  are  found  to  arise  from  the  sinus  between  the 
laterales  buds  of  figiu-e  121.  They  arise  at  first  as  a  single  bud  and  bifurcate 
later.  CaudaUy  the  most  conspicuous  trunks  are  the  dorsales,  which  arise 
in  a  median  plane  and  conspicuously  dorsal  to  the  other  posterior  trunks.  The 
dorsal  commissure  at  this  period  is  practicaUy  negligible.  The  outer- 
most ventral  tnmk-buds  are  the  laterales,  short  and  stubby  at  this 
period  of  growth.  The  ventral  trunks  arise  from  the  ventral  portion  of  the 
cerebral  masses.  Between  them  and  the  laterales  arise  trunks  which  are 
present  in  the  embryonic  stage  only.  They  may  be  designated  as  the  posterior 
intermedins  nerves. 

In  stage  11  (Fig.  122)  a  very  decided  change  has  occurred  in  the  outline  of 
the  central  nervous  system,  altho  the  fundaments  of  the  first  stage  described 
are  present.  Anteriorly  the  intermediate  space  between  the  laterales  has 
disappeared  and  from  that  region  has  arisen  a  wedge  which  is  the  fundament 
of  the  paired  dorsales.  The  ventral  trunks  have  been  set  off  to  themselves  by 
a  lateral  growth  and  elongation  of  the  intermediate  fibers.  On  the  caudal  side 
of  the  gangUon  the  posterior  dorsalis  has  been  separated  frorn  its  mate  by  the 
growth  of  the  dorsal  saddle  commissure.    Most  noticeable,  however,  is  the 


51]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  51 

change  that  has  taken  place  in  the  ventral  portion  of  the  system.  Here  the 
space  between  the  ventrales  has  become  exceptionally  wide  and  a  prominent 
commissure  has  grown  out  from  the  trunks,  commonly  known  as  the  subesopha- 
geal  commissure.  It  is  the  homolog  of  the  transverse  commissure  occuring 
along  the  entire  ventral  side.  The  intermedins  trunk  has  become  fused  with 
the  posterior  lateralis,  in  part,  and  then  crosses  over  to  the  ventralis.  This 
is  the  connection  known  in  adult  nerve  anatomy  as  the  ventrolateral  com- 
missure, a  strong  and  important  intercommunicating  trunk  (Fig.  123).  In 
the  developmental  stages  no  trace  of  palatinus  or  pharyngealis  has  been  found. 

Cercaria  glandulosa,  a  xiphidiocercaria,  is  favorable  material  for  the  study 
of  the  minute  structure  of  the  nerve  fibers  and  endings.  In  the  anterior 
end  of  this  larva  there  occur  in  five  frontal  sections  of  8/i  thickness  all  of  the 
fundamental  nerve  endings  of  this  region.  In  section  1  of  the  worm  (the 
most  dorsal  section),  there  are  no  nerve  structures  save  a  few  sensillae  to  the 
dorsal  lip  of  the  oral  sucker.  They  receive  innervation  from  the  anterior 
dorsalis,  and  derive  that  innervation  from  the  anteriormost  fibers  seen  beneath 
in  section  2,  just  in  front  of  the  musculuspreoralis.  Section  2  (Fig.  68)  shows 
the  trunk  of  the  dorsalis  descending  into  the  oral  musculature.  It  has  three 
main  branches,  one  coursing  to  the  preoral  region  to  supply  the  conductive 
strands  for  the  preoral  sensory  endings,  one  becoming  the  short  superficalis, 
and  a  longer  one,  the  profundus,  passing  under  the  endings  of  the  superficialis. 
In  the  region  of  the  musculus  preoralis,  the  apical  sensory  field  is  continuous 
across  the  sucker  from  right  to  left.  In  section  3  (Fig.  69)  are  illustrated  the 
main  outlines  of  the  central  nervous  sytem,  together  with  the  anterior  trunks. 
Here  is  the  dorsal  portion  of  the  gangUon  cells.  Anterior  and  dorsal  is  the 
dorsal  commissure  and  ventral  is  the  subesophageal  commissure.  The  for- 
ward traces  are  the  trunks  of  the  laterales  with  the  outermost  superficial  ramus 
palpalis  and  the  more  deeply  situated  ramus  muscularis.  The  latter  branch 
innervates  the  musculus  preoralis  and  the  anterior  lip  of  the  oral  sucker.  On 
the  left  is  the  trunk  of  the  anterior  ventraHs,  arising  from  below  the  mass 
of  the  ganglion  cells.  At  the  anterior  extremity  is  the  apical  sensory  field. 
The  dorsolateral  commissure  is  very  clearly  shown  in  this  section.  Section  4 
(Fig.  70)  shows  the  remainder  of  the  central  gangUa  with  the  left  anterior 
ventralis  passing  forward.  This  is  a  large  trunk,  with  an  especially  important 
ramus  palpalis  leading  to  the  apical  sensory  field,  and  a  small  oral  nervus 
communicans  supplying  the  oral  nerve  ring.  This  ring  completely  encircles 
the  superficial  region  of  the  oral  sucker  and  connects  with  the  superficial 
branch  of  the  dorsahs.  The  ramus  muscularis  of  the  ventralis  and  the  palatine 
branch  of  the  ventraHs  are  found  in  section  5  (not  figured). 

Passing  caudad  all  the  posterior  roots  are  well  defined.  Four  posterior 
roots  are  visible  in  section  3  (Fig.  69).  These  include  the  posterior  dorsales, 
laterales,  ventrales,  and  pharyngeals.  In  a  fortunately  cut  section  of  the 
same  species  the  innervation  of  the  acetabulum  is  beautifully  demonstrated 
(Fig.  71).    The  two  main  longitudinal  trunks,  the  ventrales  and  the  laterales, 


52  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [52 

are  connected  by  commissures.  Those  around  the  acetabulum  are  of  especial 
importance.  The  preace tabular  commissure  arises  from  the  lateral  trunk 
and  proceeds  in  a  posterior  oblique  course,  then  around  the  anterior  reach  of 
the  acetabulum  to  meet  the  branch  from  the  other  side.  The  postacetabular 
branch  arises  from  the  lateralis  also,  but  continues  caudad  along  the  course 
of  the  ventralis.  Behind  the  acetabulum  it  meets  the  branch  from  the  oppo- 
site side  to  form  the  span.  From  these  trunks  circumscribing  the  acetabulum 
two  ring  commissures  arise,  a  superiicialis  and  a  profundus,  of  which  the  latter 
with  the  nerve  endings  is  found  in  the  section  (Fig.  71). 

The  nervous  system  of  the  monostome,  as  worked  out  by  Jagerskiold  (1891, 
Taf.  I)  for  Ogmogaster  plicatus  (Crepl.),  has  been  substantiated  for  the  most 
part  in  the  study  of  Cercaria  pellucida  (see  figure  23).  The  three  paired 
posterior  trunks  are  evident.  The  posterior  ventralis  is  the  most  important 
of  these  and  can  be  traced  to  the  caudal  extremity  of  the  animal  in  all  cercariae 
of  this  species,  as  well  as  in  C.  konadensis  and  C.  urhanensis.  The  dorsalis  is 
less  conspicuous,  yet  it  is  usually  traceable  far  caudad.  The  posterior  lateralis 
is  delicate.  It  arises  near  the  origin  of  the  ventralis  and  swings  out  laterad  in 
a  great  bov/.  It,  too,  can  usually  be  traced  to  the  posterior  extremity  of  the 
body. 

The  anterior  trunks  can  also  be  definitely  traced.  The  ventralis  arises 
from  the  extreme  lateral  horn  of  the  ganglion  center  in  conjunction  with  the 
posterior  ventralis.  More  median,  the  anterior  lateralis  is  found.  The  two 
anterior  dorsales  arise  as  a  single  structure  along  the  median  line.  Their 
primary  function  in  the  cercaria  is  the  innervation  of  the  median  pigment  eye, 
altho  branches  may  be  traced  farther  anteriad.  Likewise,  an  important 
branch  of  each  posterior  dorsalis  constitutes  the  nerve  tract  to  the  lateral  eye. 

The  ganghon  cells  in  the  monostomes  are  superficial  to  the  nerve  strands. 
A  considerable  number  of  them  are  not  even  in  intimate  contact  with  the 
fibers,  but  have  fibrillar  communications  with  them.  The  ganglion  masses 
from  which  the  nerves  arise  are  distinctly  cornuate,  with  a  wide  dorsal  com- 
missure. 

Pigmentation  and  eye-spots  in  the  monostomes.  The  monostome  cer- 
cariae that  have  come  under  the  direct  observation  of  the  writer,  together 
with  those  described  in  the  literature,  may  be  placed  in  two  groups  according 
to  their  eye-spots,  namely,  those  with  a  single  pair  of  eye-spots,  disposed 
laterally  to  the  brain  center,  and  those  with  an  additional  median  eye,  anterior 
to  the  central  nervous  system.  The  amount  of  pigmentation  is  considerably 
larger  in  the  trioculate  species  than  in  the  binoculate  type.  Figures  1  to  3 
show  in  dorsal  view  a  series  of  stages  in  the  pigmentation  of  Cercaria  pellucida. 
The  pigment  originates  anteriorly  over  the  brain  center  and  proceeds  caudad 
along  six  lines  of  growth.  A  very  careful  study  of  the  pigmentation  in  these 
species  indicates  that  a  very  simple  but  reasonable  relation  exists  between 
the  pigmentation  and  the  underlying  nervous  system.  The  pigmentation  is 
found  to  be  a  delicate  superficial  index  of  the  underlying  nerve  fibers.    This 


531  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  S3 

pigmentation  is  present  in  the  subintegumentary  areas  and  follows  with  pre- 
cision all  the  ramifications  even  to  the  nerve  endings.  Figure  37  shows  the 
nerve  endings  in  the  anterolateral  reaches  of  Cercaria  pellucida. 

In  the  paired  eye-spot  a  definite  subspherical  "lens"  is  found  in  the  region 
of  the  concentration  of  the  pigment.  In  the  median  eye  of  the  trioculate  type 
a  "lens"  is  sometimes  present.  The  origin  of  the  eye  is  simple.  At  an  early 
stage  in  the  germ  ball  (60  n  to  80  ju),  when  the  cell  masses  of  the  nerve  trunks 
are  definitely  outlined  as  they  emerge  from  the  ganglion  center  (Fig.  36),  a 
branch  of  the  posterior  dorsalis,  larger  than  any  other  nerve,  pushes  out 
obliquely.  It  meets  an  invagination  of  the  ectodermal  layer,  which  may  be 
considered  an  "optic  cup."  There  soon  forms  in  the  hollow  of  the  cup  a 
group  of  dark  brown  refractory  granules,  which  entirely  lines  the  optic 
cup  several  layers  deep  and  leave  but  a  small  cavity  within.  The  optic  branch 
of  the  dorsalis  bends  back  into  the  cavity  at  the  place  where  it  first  comes  in 
contact  with  the  cup  and  here  ends  in  a  pyriform  enlargement,  the  nerve  cell. 
The  structure  of  this  end  organ  is  such  that  it  might  be  interpreted  as  a  "  lens, " 
if  the  connection  with  the  nerve  is  not  made  out.  Cort  (1915:15)  has  placed 
that  sort  of  an  interpretation  on  the  eye  structure  of  C.  urbanensis  and  C. 
inhabilis.  For  the  former  he  states  that  "  each  true  eye  is  formed  by  a  mass 
of  pigment  in  the  form  of  a  cup,  the  bottom  of  which  is  thicker  than  the  sides. 
A  lens  fits  into  the  opening  of  the  cup,  leaving  a  space  between  its  lower  sur- 
face and  the  bottom  of  the  cup."  And  again,  for  C.  inhabilis,  "the  large 
eyespots  .  .  .  are  composed  of  the  lens  and  the  cone  of  pigment  like  those 
already  described  for  the  monostome,  Cercaria  urbanensis.''  The  writer  has 
studied  some  of  Cort's  material  and  has  found  sections  where  such  an  inter- 
pretation might  be  made  from  a  single  section.  But  in  the  preceding  or  fol- 
lowing section  the  connection  of  this  "lens"  with  the  optic  nerve  is  plainly  seen. 

The  eye  structure  as  studied  in  this  monostome  is  similar  to  that  found 
in  the  Monogenea,  especially  the  type  in  the  posterior  eye  of  Tristommn  molae 
(Hesse,  1897:559;  Taf.  28,  Fig.  29). 

The  nervous  system  of  the  monogenetic  trematode  was  first  studied  in 
detail  by  Lang  (1880),  who  made  out  the  pigment  cup,  a  refractory  body 
(Uchtbrechender  Korper),  a  ganglion  cell,  the  retina,  and  eye  muscles  (p.  41; 
Taf.  I,  Fig.  2,  Taf.  II,  Fig.  2).  Most  later  investigators  mention  only  theper- 
ceptory  body  and  the  accessory  apparatus,  altho  Andre  (1910:217)  has  iden- 
tified the  muscle  fibers  of  Lang.  The  writer  believes  that  the  movement  of 
the  eyes  depends  largely  on  the  general  bodily  movement. 

In  the  adult  Monogenea  studied  the  pigment  cup  is  found  to  lie  between 
the  refractory  bulb  of  the  eye  and  the  possible  source  of  light  (Goto,  1894:81). 
In  the  monostomes,  as  in  Dendrocoelium  lacteum  (Hesse,  1897,  Taf.  27,  Fig. 
10),  the  hollow  of  the  cup  is  directed  outward,  so  that  light  falling  on  the  eye 
must  pass  thru  the  end  organ  before  reaching  the  inner  portion  of  the  pigment 
complex. 

The  pigment  of  the  organism  is  probably  the  waste  product  in  the  metabolic 
economy  of  the  worm.    Its  close  association  with  the  nerve  endings  in  the 


54  ILLINOIS  BIOLOGICAL  MONOGRAPHS  (54 

monostome  cercariae  seems  to  indicate  that  it  is  the  melanoidin  fraction  of 
the  oxidative  processes  in  the  nervous  system.  The  possibility  of  utility  as 
a  receptor  of  light  or  heat  is  a  secondary  item  and  must  not  be  confused  with 
the  primary  meaning  of  the  pigmentation. 

In  the  free-Uving  Platyhelminthes  the  fully  developed  eye  is  present  in  the 
mature  individual.  In  the  ectoparasitic  trematodes  the  eye-spot  is  well 
developed  in  the  young  animal  (Hesse,  1897:560,  561),  but  degeneration  takes 
place  as  the  animal  matures.  Goto  (1894:81),  speaking  of  Tristomum,  ob- 
serves: "Morphologically  speaking  they  are  certainly  degenerate  eyes;  and 
have  probably  been  derived  from  such  eyes  as  are  found  in  Turbellaria;  but 
I  do  not  think  they  are  functional.  In  the  first  place  the  pigment  granules 
are  situated  on  the  dorsal  side  and  thus  prevent  the  light  from  reaching  the 
lens,  since  the  dorsal  side  is  the  only  direction  from  which  light  can  come.  In 
the  second  place  there  is  not  always  a  distinct  retina.  If  these  'eyes'  are 
really  still  useful  to  the  animal,  they  may  possibly  be  a  temperature  sense 
organ;  and  for  that  purpose  their  structure  seems  to  answer  well."  Goto 
goes  on  to  show  that  the  more  degenerate  condition  of  the  eyes  in  Tristomum 
ovale  is  due  to  the  greater  degree  of  internal  parasitism  of  this  species  than 
that  of  Tristomum  molae.  In  the  monostome,  the  eyes  are  well  developed  in 
the  cercaria  but  become  fully  degenerate,  with  a  loss  of  all  the  pigment  in  the 
adult,  so  that  the  adult  of  one  species  has  been  described  by  Creplin  as  "albi- 
dus"  (Jagerskiold,  1891 :4).  In  some  species  of  Allocreadiidae  {Crepidostomum 
farionis  O.  F.  M.  and  C.  cornutum  (Osborn)),  pigment  eye-spots  are  found  in 
the  adult.  A  still  further  stage  of  degeneracy  is  found  in  Cercaria  racemosa 
(Fig.  100)  and  C.  gracillima  (Fig.  144),  where  the  optic  nerve  is  still  present 
but  the  pigmentation  is  absent. 

In  Cercaria  gracillima,  the  representative  of  the  furcocercariae,  the  ner- 
vous system  is  narrow,  in  correspondence  with  the  attenuate  condition  of  the 
animal.  The  posterior  laterales  are  not  found  in  the  mature  cercariae,  altho 
the  bud  is  present  in  the  germ  ball  (Fig.  151).  One  is  struck  by  the  significant 
resemblance  of  the  main  nerve  complex  of  this  cercaria  and  that  of  Schistosoma 
haematobium,  described  in  detail  by  Looss  (1895).  The  three  pairs  of  anterior 
trunks  are  readily  made  out,  altho,  in  addition,  a  prominent  dorsolateralis  is 
found  (Fig.  150).  The  posterior  dorsalis  arises  from  the  dorsal  side  of  the 
ganglion  cell  mass  and  proceeds  caudad  to  the  region  of  the  acetabulum,  where 
it  fuses  with  the  ventral  trunk.  A  prominent  subesophageal  commissure  and 
a  small  pharyngealis  are  present.  The  fundamental  resemblance  between 
the  system  described  for  this  cercaria  and  that  for  the  schistosome  adult 
seems  to  the  writer  to  be  sufficient  morphological  evidence  for  the  correlation 
of  these  apharyngeal  furcocercariae  with  the  Schistosomatidae. 

A  study  of  the  nervous  system  of  the  Holostomata  has  been  made  of  Cer- 
caria ptychocheilus,  based  on  both  toto  mounts  and  sections  (Fig.  53).  No 
adequate  idea  of  the  nervous  system  of  this  group  can  be  secured  from  the 
meager  data  of  Brandes  (1891)  and  Thoss  (1897).    The  dorsal  commissure  is 


55]  LIFE  HISTORY  OF  TREMATODES— FAUST  55 

indistinct  and  thoroly  fused  with  the  ganghon  masses.  The  latter  are  wide, 
with  a  construction  in  each  in  the  region  of  the  origin  of  the  lateral  trunks. 
The  trunks  figured  by  Thoss  are  probably  the  ventrales,  since  they  supply  the 
main  innervation  of  the  animal.  The  anterior  ventralis  arises  along  with 
the  posterior  ventraHs  just  anterior  to  the  latter.  The  anterior  trunk  soon 
divides.  The  major  portion  runs  around  the  oral  sucker,  while  the  external 
branch  is  traceable  anterolaterad.  The  anterior  lateralis  is  represented  by  a 
blunt  stock  just  outside  the  pharynx.  It  rims  cephalad  but  soon  ends  in  two 
delicate  branches.  There  is  no  posterior  dorsal  of  posterior  lateral.  The 
posterior  ventral  is  stout  and  thick.  It  gives  off  one  prominent  branch  ex- 
ternally soon  after  it  reaches  its  most  external  position.  At  regular  intervals 
it  gives  off  branches  internally  which  have  the  indication  of  rudiments  of 
commissures.  These  transverse  trunks  just  anterior  and  posterior  to  the 
acetabulum  are  still  well  developed;  they  are  similar  to  those  described  for 
the  distome. 

Contrary  to  the  opinion  of  Looss  (1894:245,  246),  the  writer  has  found 
without  exception  that  the  general  trematode  nerve  anatomy  can  be  traced 
from  the  early  germ  balls  up  thru  various  stages  of  growth,  and  that  the 
cercaria  shows  not  only  the  potentialities  of  the  adult  system,  but  actually 
the  details  of  this  system.  Moreover,  the  study  of  various  groups  of  cer- 
cariae  has  demonstrated  that  the  fundamental  deviations  and  modifications 
from  type  are  recognizable  in  the  mature  cercaria.  Thus  this  study  has 
shown  that  the  nervous  system  of  the  cercaria  is  constant  for  the  group  to 
which  it  belongs,  and  is  a  definite  basis  for  the  natural  classification  of  the 
groups. 

In  contrast  to  the  highly  developed  nervous  system  found  in  the  cercaria 
is  that  of  the  parthenita.  In  the  sporocyst  no  definite  nerve  complex  is  found, 
altho  Looss  (1892)  has  observed  nerve  elements  in  miracidia  of  Amphistomum 
subdavatum.  In  the  redia,  however,  with  the  continued  functioning  of  the 
highly  muscular  pharynx,  there  is  a  nerve  complex  practically  embracing  the 
entire  anterior  portion  of  the  gut  (Fig,  125).  Viewed  from  the  dorsal,  ventral, 
or  lateral  aspect,  the  system  in  surface  view  appears  as  an  H.  It  is  resolvable 
into  four  anterior  trunks,  four  posterior  trunks,  and  a  ring  commissure.  On 
the  dorsal  side  are  two  swellings,  the  rudiments  of  the  cerebral  ganglion  masses 
of  the  cercaria.  The  nerve  cells  of  the  system  are  very  prominent.  They 
are  usually  bipolar  or  multipolar  (Fig.  126),  but,  as  might  be  expected,  the 
more  superficial  ones  are  more  often  the  multipolar  cells. 

This  redia  nervous  system  constitutes  a  very  primitive  type,  in  which  the 
nerve  cells  are  much  more  frequently  diffuse  and  more  discrete  than  in  the 
systems  in  the  cercariae.  It  is  probable  that  the  pharynx  is  responsible  for 
keeping  the  system  from  total  degeneration. 

The  size,  number,  and  location  of  the  ganglion  cells  vary  according  to  indi- 
vidual species  of  cercariae.  They  may  be  situated  within  the  ganghon  centers, 
as  in  Cercaria  micropharynx  (Fig.  97)  and  C.  glandulosa  (Figs.  69,  70);  they 


56  ILUKOIS  BIOLOGICAL  MONOGRAPHS  {56 

may  be  scattered  around  the  ganglia  altho  not  imbedded  in  the  fibers.  In 
the  redia  of  C.  trisolenata  the  fibers  are  less  conspicuous  than  the  ganglion 
cells.  Species  closely  related  may  have  ceUs  of  different  numbers  and  different 
sizes.  In  C.  micro  pharynx  there  are  always  just  two  ganghon  cells,  imbedded 
in  the  fibers,  just  above  the  esophagus.  Their  nuclei  are  large,  pyriform, 
and  usually  containing  conspicuous  refractory  nucleoli.  They  measure  5.5^i 
to  6ju  in  short  diameter  by  8.5^  to  9/i  in  long  diameter.  The  nucleoli  are 
about  2/i  in  diameter.  Cercaria  glandulosa  presents  a  case  where  there  is  a 
definite  number  of  minute  ganghon  cells  within  the  ganghon  masses.  There 
are  fifteen  cells  in  each  of  the  two  masses.  The  cell  walls  are  not  well  defined, 
but  the  nuclei  are  readily  distinguished.  They  measure  1/x  to  1.5/x  in  short 
diameter  by  1.5m  to  2/i  in  long  diameter.  The  ganghon  cells  of  C.  pellucida 
are  numerous;  it  has  not  been  ascertained  whether  they  are  constant  in  ntmi- 
ber.  They  are  subspherical  at  times,  but  are  usually  multipolar.  The  entire 
cell  averages  3.Zti  by  6n  while  the  nuclei  measure  Iju  to  \.6n.  The  ceUs  of  the 
redia  of  C.  trisolenata  are  usually  multipolar  in  the  region  of  the  epidermis. 
They  range  from  6n  to  22/i  in  diameter.  The  nuclei  are  inconstant  in  size, 
varying  from  2/i  to  6/i  in  diameter.  The  nuclei  of  the  ganghon  cells  of  C. 
gracillima  are  so  minute  in  the  nerve  complex  in  the  germ  balls  (Fig.  151)  that 
they  are  barely  visible  under  1,000  magnification.  Yet  these  nuclei  are 
definitely  set  off  from  the  surrounding  matrix.  They  measure  about  0.4/* 
in  diameter. 

In  cell-studies  of  adult  trematodes  the  nerve  cells  have  been  measured  in 
many  cases.  The  measurements  range  from  80/i  (Lejtemd,  1881:41)  in  Gas- 
trodiscus  polymastos  to  6/x  (Fischer,  1883:17)  in  Opisthotrema  cochleare.  The 
nuclei  range  from  12/x  (Juel,  1889:41)  in  Hemiurus  excisus  to  l.tfi'va.  Opistho- 
trema cochleare  (Fisher).  A  comparison  of  these  measurements  in  adult 
trematodes  with  those  for  the  cercariae,  shows  that  the  nuclei  of  the  adult 
cercariae  are  as  large  as  those  of  the  adult  trematode.  It  is  evident,  however, 
that  the  cells  are  much  smaller  in  the  cercariae.  Ageing  of  these  cells  consists, 
then,  in  the  growth  of  the  cytoplasm  rather  than  an  increase  in  size  of  the 
nucleus. 


S7J  LIFE  HISTORY  OF  T REM ATODES— FAUST  57 


DESCRIPTION  OF  THE  TREMATODES   INFECTING    MOLLUSKS 
OF  THE  BITTER  ROOT  VALLEY 

INTRODUCTION 

On  account  of  the  biological  isolation  of  the  Bitter  Root  Valley,  it  is  little 
wonder  that  it  contributes  new  species  of  trematodes.  The  fourteen  species 
of  trematodes  found  in  the  valley  are  not  thot  to  comprise  the  entire  trematode 
fauna  of  the  region,  but  are  the  representative  species  for  the  year  and  season 
when  the  study  was  made.  Of  the  fourteen  species  found  in  the  Bitter  Root 
River,  two  are  larval  Monostomata,  two  are  Holostomata,  and  the  remaining 
ten  are  Distomata.  In  addition  to  these,  a  larval  holostome,  Tetracotyle 
pipientis  nov.  spec,  from  the  vicinity  of  Chicago,  Illinois,  is  included  in  the 
study  for  the  sake  of  comparison. 

Previous  to  the  writers'  preliminary  report  (Faust  1917)  the  following 
larval  trematodes  have  been  described  for  North  America. 
Monostomata  Distomata 

Cercaria  hyalocatida  Haldemann  1842  Cercaria  polyadena  Cort  1914 

Glenocercaria  liicania  Leidy  1877  Cercaria  hemilophura  Cort  1914 

Cercaria  urbanensis  Cort  1914  Cercaria  trigonura  Cort  1914 

Amphistomata  Cercaria    trivohis    Cort    1914 

Cercaria  inhabilis  Cort  1914  Cercaria  rubra  Cort  1914 

Cercaria  diastropha  Cort  1914  Cercaria  douthitti  Cort  1914 

Cercaria  gorgonocephala  Ward  1916  Cercaria  wrightii  Ward  1916 

Distomata  Cercaria  anchoroides  Ward  1916 

Cercaria  agilis  Leidy  1858  Cercaria  marcianae  La  Rue  1917 

Rhopalocerca  tardigrada  Leidy  1858  (Really  a  Distomulum) 

Gymnocephala  ascoidea  Leidy  1877  Cercaria   vergrandis  La  Rue  1917 

Cercaria  platyura  Leidy  1890  (Really  a  Distomulum)     . 

Cercaria  reflexae  Cort  1914  Holostomata 

Cercaria  megalura  Cort  1914  Diplostomulum  cuticula  (v.  Nordmann  1832) 

Cercaria  leptacantha  Cort  1914  Diplostomulum  grande  (Diesing  1850) 

Cercaria  caryi  Cort  1914  Diplostomulum  volvens  (v.  Nordmann  1832) 

Cercaria  isocotylea  Cort  1914  Tetracotyle  typica  (Diesing  1858) 

Cercaria  brevicaeca  Cort  1914  Diplostomulum  parmdum  (Stafford  1904) 

Cercariaetim 

Cercariaeum  helicis  (Leidy  1847)    Later  recorded  by  Leidy  as  C.  vagans  (1850). 

In  addition,  there  is  the  doubtful  form,  Cercaria  bilineata  Haldemann  1840. 

According  to  Stiles  and  Hassall  (1908:157),  Leidy  is  credited  with  the 
record  of  a  species,  Diplostomulum  rhachiaeum  (Henle).  Investigation  of  the 
literature  shows  this  to  be  an  error,  owing  to  the  confusion  of  the  names 
Leidy  and  Leydig.  Fr.  Leydig  described  the  species  D.  rhachiaeum  for  Europe 
in  1853  (Leydig,  1853:383). 

Of  the  thirty-two  forms  listed,  it  is  doubtful  if  any  except  those  described 
by  Cort  (1914),  Ward  (1916)  and  LaRue  (1917)  could  be  recognized  by  their 
descriptions,  since  in  the  majority  of  cases  the  data  are  so  indefinite  as  to  leave 
the  systematist  a  wide  range  of  choice  in  determining  the  species.    An  excellent 


58  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [58 

example  of  this  valueless  type  of  description  is  afforded  in  the  form  Diplosto- 
mulum  cuticula  (von  Nordmann  1832),  reported  by  four  American  investigators 
from  various  localities  east  of  the  Rocky  Moimtains.  The  descriptions  include 
larvae  encysted  with  pigment  and  without  it,  some  specimens  found  subder- 
mally,  others  taken  from  the  peritoneum  of  the  body  cavity,  all  secured  from 
a  great  variety  of  teleost  fishes.  In  none  of  the  descriptions  is  there  mention 
of  the  course  of  the  excretory  system  or  of  the  genital  cell  masses,  both  of  which 
are  essential  to  the  exact  determination  of  the  species.  It  seems  reasonably 
certain  that  a  careful  revision  of  these  forms  described  as  Diplostomulum 
cuticula  (von  Nordmann)  would  result  in  the  discovery  of  several  new  species 
of  Diplostomulvun. 

The  species  of  cercariae  and  parthenitae  described  in  this  section  of  the 
paper  have  been  studied  with  special  reference  to  the  excretory,  genital,  and 
nervous  systems. 

MONOSTOMATA 

Cercaria  pellucida  Faust  1917 

This  larval  trematode  is  a  muscular  cercaria,  characterized  by  heavy 
anterior  pigmentation  on  the  dorsal  surface,  centered  around  three  foci,  the 
paired  lateral  eye-spots  and  the  median  eye.  It  is  a  member  of  the  trioculate 
group  of  the  Monostomata.  The  pigmentation  tends  to  spread  caudad  from 
the  pigment  center  along  six  Hues  of  growth,  two  dorsal,  two  lateral  and  two 
ventral.  These  lines  of  pigment  have  been  shown  (p.  53)  to  be  the  superficial 
index  of  the  underlying  nerve  trunks.  The  worm  is  characterized  by  1)  a 
transparent  body,  2)  a  circuit  of  refractory  granules  that  marks  the  excretory 
system,  3)  a  small  oral  sucker,  and  4)  large  longitudinal  muscle  bimdles  of 
the  tail. 

Cercaria  pellucida  was  obtained  from  Lymnaea  proxima  Lea  in  the  Bitter 
Root  River  in  the  vicinity  of  Corvallis,  Montana,  and  from  Physa  gyrina  Say 
near  Buckhouse  Bridge.  The  snails  were  examined  in  October,  1916. 
Lymnaea  proxima  contained  a  heavy  infection  with  this  species,  along  with  a 
lesser  infection  with  the  monostome  cercaria,  C.  konadensis,  and  a  distome 
larva,  C.  diaphana.  Physa  was  heavily  infected  with  an  echinostome,  C. 
trisolenata,  and  contained  only  a  hght  infection  with  the  monostome.  In  all 
cases  the  infected  organs  were  the  Uver  ceca. 

The  mature  C.  pellucida  has  an  average  measurement  of  0.4  mm.  to 
0.7  mm.  in  length  and  0.18  mm.  to  0.2  mm.  in  width.  The  tail  is  about  0.5 
mm.  long  and  has  a  diameter  of  0.07  mm.  at  the  base.  Most  usually  the 
animal  has  an  eUiptical  constricted  outline,  such  as  is  shown  in  figiu-e  4,  but 
when  relaxed  it  assumes  the  elongate-ovoid  or  spatulate  condition,  shown  in 
figures  1  to  3. 

The  parthenita  is  a  large  conspicuous  redia,  measuring  2.2  mm.  by  0.5  mm. 
(Fig.  6).  Within  the  redia  is  a  large  rhabdocoel  gut  extending  almost  the 
entire  length  of  the  animal  and  measuring  0.3  mm.  in  cross  section.  The  gut 
empties  anteriad  thru  a  muscular  bulbus  15m  in  length  and  12/x  in  cross  sec- 


591  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  59 

tion.  It  is  spinose  internally  (Fig.  20).  In  the  prepharynx  region  is  a  unique 
piercing  organ  (Fig.  17),  probably  of  ectodermal  origin.  It  is  four-lobed  and 
is  covered  with  spines.  A  rythmic  eversion  of  the  organ  against  the  host  tissue 
and  redrawal  within  the  pharynx  region  of  the  parthenita  is  a  characteristic 
movement  of  the  redia.  Around  the  muscular  pharynx  is  a  ganglion  mass 
consisting  of  a  fibrous  matrix  and  a  network  of  ganglion  cells.  Behind  the 
head  region  is  a  neck-like  constriction,  and  behind  the  neck  is  a  sacculate 
body.  At  the  extreme  posterior  end  is  a  large  papilla.  The  redia  is  covered 
with  a  non-cellular  basement  membrane,  and  imbedded  in  this  superficially  in 
the  form  of  minute  tuberosities  are  the  remains  of  the  epidermal  nuclei 
(Fig.  22). 

The  walls  of  the  redia  are  well-supplied  with  muscular  layers,  longitudinal 
and  transverse,  so  that  the  parthenita  is  capable  of  extraordinary  distension 
and  contraction,  altho  it  has  no  specific  locomotor  organs. 

The  germ  balls  of  the  redia  arise  from  the  matured  ova,  derived  from  four 
cells  localized  at  the  posterior  extremity  of  the  parthenita.  Altho  the  cells 
lying  next  to  the  wall  around  this  quartet  may  be  potentially  germ  cells,  they 
take  no  part  in  the  ordinary  proliferation  of  germ  cells  (Fig.  22).  From  these 
cells  arise  the  germ  balls,  thru  cleavage  into  2,  3  and  5  cells,  after  which  cer- 
tain cells  of  the  ball  appear  much  smaller  than  the  others  and  grow  over  the 
latter,  giving  rise  to  the  gastrula  by  epiboly.  The  young  germ  balls  usually 
lie  en  masse  behind  the  gut,  while  the  more  advanced  cercariae  are  crowded 
anteriorly.  They  appear  strangely  grotesque,  with  their  pigment  eyes  and  their 
snout-like  bodies  oscillating  back  and  forth  within  the  body  wall  of  the  par- 
thenita. 

Aside  from  the  larger  size  of  the  body  and  the  trioculate  anterior  end, 
Cercaria  pellticida  might  be  at  first  confused  with  Cercaria  urhanensis  Cort. 
While  the  size  and  eye-spots  are  sufficient  to  separate  these  two  species,  a 
more  careful  examination  shows  that  there  has  not  been  a  separation  of  two 
species  at  all,  but  more  correctly  two  groups  of  species.  The  group  of  smaller 
species  is  binoculate  and  ranges  around  0.3  mm.  to  0.46  mm.  in  length  by  0.1 
mm.  to  0,16  mm.  in  width,  while  the  group  of  larger  species  is  trioculate  and 
averages  around  0.5  mm.  in  length  by  0.15  mm.  to  0.2  mm.  in  width.  Con- 
sequently from  a  description  of  external  characters  alone  there  is  no  means  of 
separating  Glenocercaria  lucania  Leidy  from  the  Bitter  Root  species  Cercaria 
pellucida.  It  is  such  a  problem  as  this  that  has  caused  the  writer  to  believe 
that  there  are  characters  more  deeply  seated  in  the  larva  that  will  readily 
set  it  off  from  others  of  the  same  group. 

Sufficient  care  in  technic  makes  it  possible  to  bring  out  very  clearly  and 
convincingly  the  genital  organs  of  the  Bitter  Root  species.  Here  are  characters, 
constant  both  in  the  larva  and  the  adult  that  readily  differentiate  these  mon- 
ostome  cercariae.  These  have  been  described  in  detail  in  the  section  devoted 
to  morphology  (p.  45)  and  need  only  to  be  summarized  at  this  point.  The 
median  ovary  just  in  front  of  the  excretory  bladder  opens  out  thru  a  short 
duct  at  its  left  (Fig.  18),  and  after  receiving  the  common  vitelline  duct,  opens 


60  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [60 

anteriad  into  the  uterus.  This  organ  has  an  outlet  just  behind  the  median 
eye.  It  ends  in  a  poorly  developed  vagina.  No  Laurer's  canal  has  been 
definitely  made  out  in  the  totos  but  there  is  evidence  of  such  an  organ  in  sec- 
tions. From  the  sides  and  sUghtly  caudad  to  the  ovary  the  closely  massed 
testes  open  into  filiform  vasa  efferentia  which  unite  anterior  to  the  ovary  to  form 
the  vas  deferens.  This  canal  is  directed  forward  parallel  to  the  uterus,  ending  in 
a  bulbous  cirrus  pouch  just  to  the  left  of  the  vagina.  The  three  paired  outer 
vitelline  follicular  masses  and  the  five  paired  iimer  masses  occupy  a  dorsal 
position.  They  are  irregular  in  contour  (Fig.  4),  with  aciculate  margins,  and 
are  finely  granular  with  close  massing  of  the  granules.  Inconspicuous  com- 
mon viteUine  ducts  connect  the  vitellaria  with  the  ootype  just  dorsal  to  the 
ovary. 

The  excretory  trunks  are  similar  to  those  of  the  entire  group  of  monostomes. 
The  bladder  is  quite  small,  48/i  in  section,  moderately  muscular,  superficially 
triangular,  with  the  excretory  pore  posterior.  The  excretory  tube  in  the  tail 
is  vesicular  at  the  base  and  narrows  down  distad  (Fig.  4).  The  tubes  of  the 
tnmk  are  crowded  with  large  excretory  granules. 

The  digestive  system  is  t3T)ically  triclad,  with  ceca  extending  to  the  sub- 
distal  extremity.  They  are  filled  with  a  jell,  and  are  crowded  with  granules 
imbedded  in  the  jell.  No  pharynx  has  been  observed.  The  oral  sucker  is 
directed  ventrad.     It  is  small  but  powerful. 

The  parenchyma  is  filled  with  cystogenous  granules,  included  in  one-celled 
cystogenous  glands,  probably  of  mesodermal  origin  (Fig.  14).  Between  the 
cystogenous  cells  are  angular  parenchyma  cells,  more  commonly  known  as 
vesicular  cells  (Blasenzellen),  with  processes  extending  to  the  integiunent  and 
possibly  functioning  in  the  capacity  of  secretory  ducts  for  the  basement  mem- 
brane. 

The  locomotor  organs  at  the  posterior  angles  of  the  tnmk  are  neither  spicu- 
late  nor  spinose.  They  possess  no  cement  glands.  The  tail  has  no  central 
pair  of  gland  elements  such  as  axe  found  in  binoculate  cercariae  of  the  mono- 
stome  group.  However,  the  ordinarj'  parenchyma  cells  of  the  tail  of  C.  pelltt- 
cida  are  remarkably  large  and  vesicular  and  suggest  a  glandular  function 
(Fig.  19.). 

Large,  isolated  bands  of  transverse  muscle  fibers  are  present  thruout  the 
body  just  within  the  basement  membrane.  Longitudinal  muscles  are  not  so 
large  in  the  tnmk  as  are  the  transverse  series,  but  constitute  the  important 
muscle  system  of  the  tail.  The  transverse  muscles  of  the  tail  frequently  give  a 
moniliform  appearance  to  that  organ,  such  as  is  described  by  Leidy  (1877)  for 
Glenocercaria  Iticania. 

The  nervous  system  of  C.  pellucida  (Fig.  23)  varies  from  the  distome  nervous 
system  only  in  its  relation  to  pigmentation  and  the  eye-spots.  There  are  six 
anterior  tnmks  and  six  posterior  trunks  arising  from  a  paired  brain  center. 
They  constitute  the  dorsal,  lateral  and  ventral  nerve  lines.  These  trunks  are 
carefully  followed  by  the  melanoidin  pigment  fraction.    The  eye-spots  receive 


61]  LIFE  HISTORY  OF  TREMATODES—FAUST  61 

innervation  from  the  dorsal  trunks;  the  paired  eyes  are  innervated  from  the 
posterior  trunks  and  the  median  eye  from  the  fused  branch  of  the  anterior 
dorsales.  The  optic  nerve  runs  forward  from  its  origin  in  the  dorsalis  and 
enters  the  pigment  cup  from  above,  ending  in  a  sensory  cell  (Fig.  24).  The 
general  anatomy  and  histology  of  this  eye-spot  is  similar  to  that  described  for 
all  Turbellaria  and  Monogenea.  However,  no  previous  account  has  been 
found  for  the  structure  of  the  eye-spot  of  the  Digenea  showing  its  relation  to  the 
central  nervous  system. 

Locomotion  is  brought  about  thru  a  cooperation  of  the  body  musculature 
together  with  the  special  functioning  of  the  oral  sucker  and  the  posterior  loco- 
motor pockets.  The  tail  serves  as  a  swimming  organ,  with  a  peculiarly  rapid 
and  nervous  lashing. 

Encystment  occurs  as  a  fmal  step  in  the  larval  stage  of  the  life-history  of 
the  hermaphroditic  generation,  in  preparation  for  entering  the  definitive  host. 
The  process  is  rapid  and  the  mucoid  cyst  is  secreted  by  the  cystogenous  glands 
before  the  tail  has  been  thrown  off.  This  organ  is  freed  from  the  cyst  by  the 
violent  wriggling  which  it  produces.  The  cyst  is  spherical;  it  encloses  the  now 
quiescent  larva.  The  outer  portion  of  the  cyst  is  an  opaque  mucoid,  which 
gives  the  cyst  an  appearance  of  a  white  grain,  about  the  size  of  a  pin-head. 
The  larva  now  waits  transfer  to  the  definitive  host. 

Cer carta  konadensis  Faust  1917 

Cercaria  konadensis  is  a  species  of  monostome  cercaria  of  the  binoculate 
type.  The  species  is  more  graceful  than  C.  pellucida.  Its  bodily  contour 
is  most  usually  spa  tula  te,  while  the  long  tail  reaches  far  behind.  The  small 
amount  of  pigmentation  around  the  two  eye-spots  and  the  less  usual  pigmenta- 
tion along  the  nerve  trunks  caudad  serve  to  indicate  the  superficial  differences 
between  the  binoculate  group  to  which  this  form  belongs  and  the  trioculate 
group. 

Cercaria  konadensis  was  found  in  Lymnaea  proxima  Lea,  collected  from  the 
Bitter  Root  River  at  Corvallis  Montana  in  October  1916.  It  occurred  as  an 
infection  along  with  the  larger  species,  C  pellucida.  Of  the  snails  examined, 
31.3  per  cent  were  infected  with  this  cercaria  in  the  connective  tissue  be- 
tween the  liver  ceca.  The  cercaria  measures  0.4  mm.  to  0.46  mm.  in  length 
and  has  a  bodily  width  of  0.1  mm.  to  0.16  mm.  (Fig.  25).  The  tail  is  of  equal 
length  under  conditions  of  relaxation,  but  may  be  extended  so  as  to*exceed 
by  far  the  bodily  length.  At  its  base  it  has  a  transverse  diameter  of  30/x  to 
40jU.  The  posterior  locomotor  organs  are  not  so  conspicuously  lateral  as 
those  of  C.  pellucida  (Fig.  4).  Considered  together  with  the  younger  stage 
of  C.  pellucida  (Fig,  12),  these  pockets  suggest  an  origin  from  the  caudal 
pockets  found  in  certain  distome  cercariae.  Unlike  those  of  C.  pellucida,  the 
posterior  locomotor  pockets  of  C.  konadensis  are  provided  with  about  ten 
gland  cells  surrounding  the  lumen,  cells  probably  of  a  secretory  nature  (Fig. 
21). 


62  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [62 

The  parthenita  (Fig,  26)  is  a  relatively  small,  elongate  redia,  1.7  mm.  in 
length  and  0.35  mm.  in  transverse  section  near  the  middle.  It  is  attenuately 
obtruncate,  with  the  posterior  end  sloping  down  to  a  blunt  point.  The 
pharynx  is  muscular  but  small,  60)u  in  cross  section,  and  aspinose  internally 
(Fig.  31).  The  rhabdocoel  gut  extends  posteriad  about  three-fifths  the  body 
length.  The  posterior  end  is  filled  with  cells,  composed  of  a  central  rachis 
with  apex  directed  posteriad,  and  an  outer  cell  complex  of  goblet  cells  (Fig.  30). 
The  central  rachis  comprises  the  germinal  epitheUum,  the  proliferating  region  of 
which  is  situated  sub  terminally.  From  this  epithelial  mass  the  matured 
parthenogenetic  eggs  are  proliferated  forw'ard  so  that  the  germ  balls  come  to 
lie  in  the  lumen  posterior  to  the  gut.  Similarly  to  those  in  C.  pdlucida,  only 
the  maturing  cercariae  come  to  lie  around  the  gut. 

The  excretory  system  of  C.  konadensis  consists  of  the  circuitous  trunk 
system,  opening  posteriorly  into  a  non-muscular  vesicular  bladder.  This 
vesicle  measures  16)Lt  to  17/i  in  width  and  14/i  to  15^  along  the  longitudinal 
axis  of  the  cercaria.  The  excretory  pore  is  dorsal,  opening  from  the  middle 
of  the  bladder  (Fig.  29). 

The  digestive  system  is  of  the  usual  triclad  tjpe,  with  no  distinct  pharyn- 
geal region. 

The  genital  organs  are  notocotyhd  in  character,  but  different  in  several  fea- 
tures from  those  of  C.  pellucida.  The  ovary  (Fig.  28)  is  skull-cap  shaped,  with  a 
distinct  Laurer's  canal.  A  short  oviduct  leads  into  the  ootype.  The  uterus, 
emerging  from  the  ootype,  runs  cephalad,  ending  in  a  swollen  vagina  some 
distance  behind  the  line  joining  the  paired  eye-spots.  The  vitellaria  consist 
of  a  double  series  of  five  inner  and  three  outer  follicular  masses.  The  indi- 
vidual glands  are  very  diffuse  and  dendritic. 

The  testes  are  small,  lateral,  and  posterior  to  the  ovary,  with  the  vasa 
efferentia  describing  a  broad  crescent  anteriad  around  the  ovary  and  meeting 
in  a  common  tube,  the  vas  deferens,  which  runs  forward  to  the  left  and  parallel 
to  the  uterus.    The  vas  deferens  ends  in  a  swollen  cirrus  pouch  (Fig.  25). 

The  nervous  system  corresponds  to  the  monostome  type  described  for  C. 
pellucida,  except  that  the  dorsal  trunk  to  the  median  pigment  eye-spot  is 
lacking. 

In  the  tail  six  paired  groups  of  gland  cells,  derived  from  parenchyma, 
occupy  places  just  lateral  to  the  median  canal  of  the  excretory  system,  each 
group  dove-tailing  into  the  one  next  proximal.  These  caudal  glands  indicate 
a  much  closer  kinship  of  this  worm  to  Cercaria  urbanensis  than  to  C.  pellucida. 

Encystment  is  brought  about  by  the  pouring  out  of  the  contents  of  the 
cystogenous  cells  and  by  subsequent  decaudation. 

HOLOSTOMATA 

Cercaria  flabelliformis  Faust  1917 

Cercaria  flabelliformis  is  the  first  larval  holostomid  to  be  described  in 
detail  for  North  America.    Leidy  has  listed  Tetracotyle  typica  Diesing  from 


63]  LIFE  EISTOR  Y  OF  TREMA  TODES—FA  UST  63 

Lymnaea  catascopium  and  Fkysa  heterostropha  (1890).  Rettger  (1897)  has 
mentioned  a  larval  tetracotyle  in  connection  with  a  life-history  study,  but  he 
has  failed  to  identify  the  species. 

Cercaria  flabelliformis  was  found  in  three  collections  of  Physa  gyrina  Say, 
taken  from  the  Bitter  Root  River  in  the  vicinity  of  Corvallis,  Montana,  in 
October  1916.  Practically  every  snail  from  these  collections  bore  evidence 
of  infection  with  the  parthenita  of  this  species,  altho  only  14.7  per  cent  of  the 
snails  examined  contained  the  tetracotyle.  The  mature  cercaria  has  a  length 
of  0.48  mm.  to  0.56  mm.,  and  a  width  of  0.44  mm.  It  is  about  0.2  mm.  thick. 
While  the  anterior  end  is  not  clearly  set  oflf  from  the  posterior  end  as  is  usual 
in  holostomids,  it  does  have  the  suctorial  cup  which  includes  all  the  ventral 
suctorial  apparatus,  including  among  the  rest  the  lateral  suctorial  grooves. 
In  the  young  larva  these  lateral  organs  are  discoidal  (Fig.  41);  in  the  mature 
tetracotyle  they  have  become  modified  into  lateral  lappets  (Fig.  40). 

The  larva  was  found  maturing  within  the  redia,  free  in  the  liver  interstices, 
and  encysted  in  the  Hver  tissues.     It  was  seldom  found  free  in  the  tissues. 

The  parthenita  (Fig.  42)  is  a  redia  which  measures  0.5  mm.  in  length  by 
0.052  nun.  in  transverse  section.  The  head  is  set  off  from  the  trunk  by  a  collar 
prominence,  while  in  the  posterior  third  of  the  body  are  found  the  "walking 
feet, "  which  protrude  ventrolaterad  to  support  the  redia.  The  posterior  end 
of  the  body  is  produced  into  a  large  knob,  in  which  are  parenchyma  and 
germinal  epithelium  ceUs.  At  the  oral  end  is  a  wide  muscular  organ.  It  is 
not  clear  whether  it  is  a  pharynx  or  an  oral  sucker.  It  is  about  40/i  in  trans- 
section  and  surrounds  the  fore-end  of  a  gut  0.18  mm.  long.  On  the  ventral 
side  are  two  groups  of  saHvary  glands,  six  cells  to  each  group,  opening  into  the 
anterior  region  of  the  gut  thru  a  common  duct  for  each  group  (Fig.  43). 
Around  the  anterior  end  of  the  gut,  just  behind  the  muscular  organ,  is  a  nerve 
complex  (Fig.  42),  differentiated  into  two  ganghon  masses  on  the  dorsal  side, 
four  nerve  trunks,  and  a  circimiintestinal  commissure.  A  birth-pore  is 
here  ventral  and  shghtly  sinistral.  The  wall  of  the  parthenita  is  heavily 
covered  with  an  integimient  of  non-cellular  material,  beneath  which  are 
muscle  and  parenchyma  elements.  Running  thru  the  parenchyma  is  a  com- 
plex diamond-pattern  excretory  system. 

The  germinal  epithehum  is  localized  at  the  posterior  end  of  the  redia. 
It  offers  an  unusually  fine  opportunity  for  study  of  the  maturation  of  the  ova. 
The  detailed  description  of  this  maturation  is  found  in  the  section  on  morpho- 
logy (p.  16). 

The  germ  balls  may  differentiate  into  a  second  generation  of  rediae  and  cer- 
cariae  at  the  same  time.  These  larvae  are  about  equal  in  size  as  they  develop, 
but  the  cercariae  differentiate  much  more  rapidly  than  do  the  rediae  so  that 
the  two  are  readily  distinguished.  Usually  only  three  or  four  cercariae  are 
found  developing  at  one  time  in  the  redia,  along  with  many  daughter  redia. 
This  fact  seems  to  indicate  that  the  animals  have  come  to  depend  largely  on 
parthenogenetic  propagation.    The  cercariae  escape  thru  the  birth-pore  and 


64  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [64 

soon  encyst  in  the  free  tissue  of  the  host.  The  second  generation  redia  is 
aheady  producing  germ  balls  before  it  comes  to  take  up  a  free  existence  out- 
side the  first  generation  redia. 

The  internal  systems  of  organs  of  Cercaria  flabelliformis  are  of  considerable 
interest.  However,  since  they  are  described  in  detail  in  the  respective  sections 
in  the  morphological  division  of  this  paper  (pp.  37,  45,  54)  they  will  not  be 
treated  here. 

Valuable  data  on  holostomid  anatomy  are  obtained  by  a  comparison  of 
Cercaria  flabelliformis  with  the  following  species: 

Tetracotyle  pipientis  nov.  spec. 

This  species  of  larval  trematode  was  found  in  March  1917  in  the  mesentery 
and  pericardium  of  a  large  number  of  Rana  pipiens  collected  in  the  vicinity 
of  Chicago,  Illinois.  All  of  the  frogs  were  more  or  less  infected  with  this 
holostome.  The  infection  consisted  of  creamy  oval  yellow  cysts,  either  single 
or  in  grape-like  clumps.  Each  cyst  consisted  of  many  lamellae,  and  innermost, 
a  tough  cyst  membrane.  The  inner  membrane  stains  a  deep  brown  with 
iodine  in  70  per  cent  ethyl  alcohol.  The  gross  measurement  of  the  cyst  ranges 
from  0.5  mm.  to  0.76  mm.  in  lesser  diameter  and  0.7  mm.  to  1.0  mm.  in  greater 
diameter,  while  the  inner  membrane  is  about  0.3  mm.  by  0.5  mm.  Within  the 
inner  membrane  is  the  larva,  tightly  coiled  at  one  end  of  the  cavity,  while 
the  remainder  of  the  cyst,  often  two-thirds  of  the  volume,  is  filled  with  accum- 
ulations of  large  excretory  granules.  Some  of  these  granules  have  fused  to 
form  single  clumps  as  large  as  the  larva 

WTien  the  lamellae  and  cyst  membrane  are  teased  open  and  the  larva  is 
allowed  to  work  its  way  out,  the  body  becomes  expanded  and  flattened.  It 
then  measures  0.5  mm.  in  length  by  0.37  mm.  in  trans-section  (Fig.  47).  The 
oral  sucker  is  75)U  in  diameter.  It  lies  in  an  anterior  cone  of  the  body.  Antero- 
lateral prominences  and  the  blunt  posterior  portion  of  the  body  give  a  lyrate 
outline  to  the  worm.  The  primitive  genital  pore,  80;u  in  diameter,  lies  in  a 
plane  where  the  anterior  and  posterior  portions  of  the  body  join,  just  within 
the  suctorial  pocket.  The  free  ventral  wall  of  this  pocket  is  often  folded 
backward  so  that  it  fits  down  snugly  against  the  body.  At  other  times  it 
bulges  out  so  that  the  pocket  cavity  is  a  large  ovoid  atrium.  The  acetabulum 
is  represented  by  a  single  lappet  situated  behind  the  primitive  genital  pore. 
The  non-muscular  accessory  suctorial  grooves  consist  of  long  narrow  slits, 
directed  obliquely  inward  toward  the  acetabulum.  The  entire  worm  is  covered 
with  minute  anterior  and  posterior  spines,  equally  prominent.  The  primitive 
genital  pore  is  crowned  with  a  ring  of  fused  spines.  The  lateral  suctorial 
organs  are  surrounded  by  a  band  of  discrete  spines  imbedded  in  the  tissues. 

The  worms  examined  were  all  filled  with  excretory  granules.  A  careful 
study  of  the  larva  showed  the  main  course  of  the  excretory  trunks  to  appear 
as  shown  in  figure  48.  The  median  posterior  excretory  pore,  sUghtly  dorsal, 
conmiunicates  with  the  bladder  which  merges  imperceptibly  with  the  paired 


65]  LIFE  HISTORY  OF  TREMA  TODES—FA  UST  65 

lateral  trunks.  These  tubes  lie  just  within  the  margins  of  the  larva  and  unite 
with  one  another  in  a  large  transverse  vessel  at  the  anterior  end  of  the  body, 
so  that  a  complete  circuit  is  formed.  If  a  rent  is  produced  in  the  body  near 
the  oral  sucker,  it  is  customary  for  the  excretory  granules  to  be  poured  out 
there  rather  than  thru  the  natural  channel.  A  tube  from  the  lateral  trunks 
crosses  thru  the  ventral  pocket  wall  at  its  anterior  end.  Tributary  tubules, 
bisymmetrically  arranged,  empty  into  the  main  trunks,  mostly  at  the  anterior 
and  posterior  margins  of  the  body. 

The  digestive  tract  is  simple  and  inconspicuous.  A  small  swelling  within 
the  oral  sucker  marks  the  pharynx,  just  behind  which  is  the  esophagus.  The 
ceca  barely  clasp  the  anterior  margin  of  the  primitive  genital  pore. 

The  genital  organs  are  readily  recognized  as  holostome  in  type  (Fig.  47). 
They  open  posteriad.  A  small  spherical  ovary  lies  median.  Dorsal  to  this 
is  the  ootype,  into  which  come  the  short  oviduct  and  the  transverse  vitelline 
ducts.  The  vitellaria  are  diffuse  bands  of  large  follicles  extending  from  the 
anterior  face  of  the  acetabulum  to  the  posterior  margin  of  the  genital  pouch. 
They  lie  strictly  ventral.  Two  large  oval  testes  lie  to  the  sides  of  the  ovary, 
the  one  (ti)  slightly  anterior  to  the  other  (t,).  They  have  individual  ducts 
(efferent)  which  reach  the  genital  pouch  and  fuse  into  a  common  vas  deferens 
just  before  entering  the  genital  pouch.  This  organ  is  muscular,  oval  in  con- 
tour, with  the  transverse  diameter  longer  than  the  longitudinal. 

A  survey  of  the  literature  shows  that  only  one  tetracotyle  has  been  re- 
ported for  Amphibia,  Tetracotyle  crystallina  (Rud.),  from  the  mesentery  cysts 
in  Rana  temporaria,  R.  esculanta,  Bufo  igneus,  B.  viridis,  and  Vipera  berus 
(Rudolphi,  1819:380-382).  The  formation  of  the  cysts  is  not  clearly  de- 
scribed, but  the  large  size  of  the  Europen  tetracotyle,  together  with  its  oval 
contour,  aspinose  body  and  oval  accessory  sucking  discs,  clearly  separates  it 
from  Tetracotyle  pipientis.  The  new  species  conforms  much  more  to  the  type 
represented  by  T.  cohibri  v.  Linstow,  but  differs  from  it  in  the  relative  sizes 
of  the  oral  and  ventral  suckers,  and  the  possession  of  small  spines  all  over 
the  body  instead  of  a  few  broad  spines  (Linstow,  1877:192;  Fig.  22). 

While  the  excretory  system  is  one  of  the  best  systems  of  organs  to  use  in 
systematic  work  with  trematode  larvae,  in  the  absence  of  such  data  for  other 
tetracotyles. described,  the  comparative  data  actually  afforded  are  sufficient 
in  this  case  to  justify  the  establishment  of  Tetracotyle  pipientis  as  a  distinct 
species. 

Observations  on  the  anatomy  of  Tetracotyle  pipientis  present  an  oppor- 
tunity for  comparison  with  Cercaria  flabelliformis,  the  parasite  of  the  Bitter 
Root  moUusk,  Physa  gyrina. 

The  two  larvae  are  about  equal  in  length,  but  C.  flabelliformis  is  consider- 
ably the  wider.  The  widest  region  in  T.  pipientis  is  in  the  anterior  region  of 
the  body;  the  widest  portion  of  C .  flabelliformis  is  in  the  middle  of  the  body. 
The  suctorial  pocket  in  the  former  species  has  grown  over  the  ventral  sur- 
face so  that  a  true  pocket  is  formed  with  the  opening  anterior;  in  the  latter 


66  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [66 

species  the  suctorial  pocket  is  hemispherical  with  the  opening  ventral.  The 
lateral  accessory  suctorial  grooves  in  T.  pipientis  are  non-muscular  oblique 
slits;  in  C.  jlabelliformis  they  are  at  first  oval  depressions  which  are  modified 
later  into  a  pair  of  lateral  lappets.  The  primitive  genital  pore  in  C.  fiabelli- 
formis  is  0.05  mm.  in  diameter;  in  T.  pipientis  it  is  0.08  mm.  wide,  with  a 
crown  of  heavy  spines.  The  homologies  between  the  lateral  excretory  trunks 
of  the  two  species  are  apparent,  altho  the  median  transverse  trunk  is  much 
farther  anterior  in  T.  pipientis  than  in  C.  Jlabelliformis.  The  tributar}'  tubules 
are  entirely  different  in  the  two  species.  The  digestive  ceca  of  the  Bitter 
Root  species  conform  to  the  family  type  in  extending  well  into  the  posterior 
part  of  the  body;  those  of  T.  pipientis  are  short  and  rudimentary.  The  geni- 
tal organs  of  the  two  species  occupy  the  same  relative  position,  altho  individual 
variations  in  size  and  shape  of  organs  are  evident. 

In  concluding  the  study  of  the  tetracotyle  larvae,  emphasis  must  be  placed 
on  the  maturation  of  the  parthenogenetic  ova,  which  shows  that  these  larvae 
do  not  develop  in  miracidia,  without  the  intercalation  of  parthenitae  as 
Brandes  (1891:572)  and  Fantham  (1916:224)  beUeve.  This  fact,  previously 
recorded  by  the  writer  (1917),  makes  the  morphological  evidence  complete 
in  support  of  the  view  of  true  alternations  of  hermaphroditic  and  partheno- 
genetic generations  among  Holostomata. 

Cer carta  ptychocJieUus  Faust  1917 

This  form,  really  a  Diplostomulum,  is  elongate  ovate  in  outline,  with  dorso- 
ventral  flattening,  sHght  ventral  concavity,  and  a  more  or  less  distinct  sepa- 
ration of  body  into  anterior  and  posterior  portions.  In  addition,  the 
group  to  which  this  worm  belongs  lacks  the  lateral  auxiHary  sucking  grooves 
which  are  characteristic  of  the  tetracotyle  forms.  Several  species  of  Diplosto- 
muliun  have  been  weU  described  and  their  excretory  system  beautifully  traced 
by  von  Nordmann  (1832).  These  include  the  species  Z>.  volvens,D.cuticula, 
D.  clavaium,  and  D.  breoicaudaium.  Of  the  forms  found  in  North  America 
there  have  been  recorded  D.  cuticula,  D.  volvens,  and  D.  grande  of  the  Old 
World  species,  and  D.  parvulum  (Stafford),  new  to  North  x\merica.  However, 
as  has  been  previously  suggested,  none  of  these  American  records  give  suf- 
ficient data  to  distinguish  accurately  the  species. 

The  general  outline  of  the  body  of  Cercaria  ptychocheilus  is  such  as  to  dis- 
tinguish it  readily  from  the  described  species.  Broadly  oblong-ovoid  in 
contour,  with  the  anterior  half  laminate  and  the  posterior  portion  fleshy, 
this  cercaria  might  at  first  be  confused  with  distome  cercariae.  Such  a  con- 
fusion is  caused,  further,  by  the  abbreviated  appendiculate  portion  of  the 
larva,  which,  on  extension  into  a  caudal  cone,  may  reach  one-third  of  the  body 
length,  but  on  contraction  barely  protrudes  behind  the  anterior  part  of  the 
body.  The  concavity  of  the  anterior  part  is  found  only  in  the  fleshy  region 
behind  the  acetabulum.  Here  in  this  area  is  foimd  the  muscular  complex 
comparable  to  the  cup-shaped  suctorial  apparatus  of  the  tetracotyle. 


67]  LIFE  HISTOR Y  OF  TREMA  TODES—FA  UST  67 

The  Diplostomulum  (Fig.  49)  measures  0.48  mm.  to  0.63  mm,  in  length 
by  0.17  mm.  to  0.37  mm.  in  width,  and  about  30^  thick  in  the  fleshly  portion 
of  the  body.  The  oral  sucker  is  small  but  powerful,  and  is  directed  strictly 
anteriad.  Behind  this  oral  region  the  esophagus  is  enlarged  into  the  pharynx, 
about  40/x  in  section.  Behind  the  pharynx  is  an  equal  portion  of  the  esopha- 
gus which  is  non-muscular,  posterior  to  which  the  ceca  rise,  spreading  out 
into  a  broad  furculum. 

The  acetabulum  is  large  and  circular;  it  is  situated  somewhat  posterior 
to  the  middle  of  the  body.  At  times  of  extreme  contraction  the  acetabulum 
becomes  narrowed  antero-posteriorly,  with  a  transverse  wrinkling.  This  disc 
measures  70ju  in  diameter.  The  primitive  genital  pore,  situated  just  in  front 
of  the  acetabulum,  has  lost  its  connection  with  the  genital  system  and  has 
become  modified  into  a  muscular  sucking  disc. 

The  excretory,  genital,  and  nervous  systems  have  been  treated  on  pages 
37,  45,  54,  as  types  for  the  hemistome  larva.  A  comparison  of  these  data 
with  V.  Nordmann's  observations  on  Diplostomulum  cuticula,  D.  volvens,  and 
D.  clavatum,  and  with  the  work  of  Blanchard  (1847)  on  Hemistomum  alatum 
(Goeze)  shows  the  fundamental  conformities  and  differences  of  the  excre- 
tory systems  of  the  group.  However,  the  nervous  system  (Fig.  53)  is  worked 
out  thoroly  in  this  paper  for  the  first  time  in  the  Hemistomidae.  The  genitalia 
bear  a  fundamental  resemblance  to  those  of  the  adult  species,  as  described  by 
Brandes  (1891),  but  differ  in  size,  shape  and  position  of  the  respective  organs. 
This  difference  may  be  accounted  for  in  part  by  the  immaturity  of  some  of 
the  organs,  but  there  are  undoubtedly  specific  differences,  such  as  the  lamellae 
of  muscular  nature  in  the  genital  pouch  and  the  glandular  cells  emptying  into 
the  pouch. 

The  larva  Cercaria  ptychocheilus  was  taken  from  mesentery  cysts  of  Pty- 
chocheilus  oregonensis  Richardson,  caught  in  the  Bitter  Root  River  in  April 
1915  in  the  vicinity  of  Stevensville,  and  Carlton,  Montana.  Thousands  of 
cysts  were  found.  The  cysts  are  much  larger  than  the  larvae  (Figs.  50,  51) 
and  are  filled  with  a  limpid  milky  fluid  which  bathes  the  larva  and  serves  as 
a  liquid  cushion.  The  cyst  is  oblong,  and  flattened.  It  is  composed  of  a 
thin,  tough  membrane,  and  it  is  attached  to  the  mesentery  by  a  discoid  annulus 
in  the  middle  of  one  of  the  flattened  sides.  Within  the  cyst  the  worm  works 
around  and  grows,  so  that  it  comes  to  fill  the  cyst  in  later  life.  At  frequent 
intervals  there  is  extruded  from  the  excretory  bladder  a  considerable  quantity 
of  granules  which  pile  up  at  the  posterior  end  of  the  larva  within  the  cyst, 
but  are  soon  dissolved  and  absorbed  by  the  fluid  medium. 

The  encysted  animal  when  placed  in  a  normal  saline  solution  soon  increases 
its  activity  and  bursts  thru  the  cyst.  This  rent  usually  occurs  at  one  end 
of  the  membrane.  The  larva  then  crawls  out  with  a  "measuring  worm  move- 
ment. "  After  several  hours  of  activity  it  settles  down  on  the  bottom  of  the 
container  and  remains  quiescent,  altho  sUght  mechanical  disturbances  activate 


68  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [68 

it  again.     In  a  modified  Ringer's  solution  ninety  per  cent  of  these  larvae  were 
kept  alive  for  forty-eight  hours. 

It  seems  probable  that  Cercaria  ptychocheilus  is  in  an  intercalated  host. 

DISTOMATA 

Xiphidiocercariae  (St}'let  Larvae) 
The  xiphidiocercariae  are  grouped  together  because  of  their  possession  in 
common  of  a  larA^l  stylet.    The  writer  beHeves  that  the  features  of  the  geni- 
tal and  excretory  systems  of  the  group  are  more  fundamental  characters 
which  will  hold  the  members  of  the  group  together. 

Cercaria  crenata  Faust  1917 

Cercaria  crenata  is  a  delicate  larva,  with  an  ovate  bodily  outline  and  a 
short  lanceolate  tail  (Fig.  55).  The  body  measures  0.25  mm.  in  length  by 
0.13  mm.  in  width,  and  the  tail,  0.15  mm.  to  0.16  ram.  in  length  by  lOjx  to 
30/1  at  the  base.  The  entire  body  except  the  tail  is  covered  with  minute  hair- 
like spines.  A  large  median  spine,  the  stylet  organ  (Figs.  56,  57)  hes  in  the 
dorsal  wall  of  the  oral  hood.  This  organ  is  about  SO/z  long  by  5/x  in  width  at 
its  base.  It  has  the  general  shape  of  a  quill  pen,  with  reinforcements  at  its 
base  and  also  in  the  distal  portion  toward  the  acute  point.  The  distal  third 
of  the  stylet  is  bent  ventrad  about  20  degrees.  There  are  two  prominences 
in  the  anterior  portion  of  this  organ,  one  where  the  shaft  joins  the  quill  and 
a  less  prominent  one-half  way  between  this  position  and  the  quill  point. 

The  oral  sucker  is  relatively  large,  20^  in  diameter,  while  the  acetabulum, 
situated  three-fifths  the  way  from  the  anterior  end,  measures  just  half  that 
diameter.  The  tail  is  inserted  in  the  posterior  caudal  pocket  which  has  no 
spinous  projections. 

Cercaria  crenata  was  found  in  large  numbers  in  13.6  per  cent  of  Lymnaea 
proxima  Lea,  taken  from  the  springs  at  Fort  Missoula,  Montana,  in  October 
1916.  It  occurs  in  oval  sporocyst  sacs,  0.5  mm.  in  length  and  0.35  mm.  in 
diameter.  At  one  end  the  germinal  epithelium,  is  localized  and  from  this  end 
the  ova  are  proliferated.  Only  cercariae  have  been  found  to  develop  within 
the  sporocysts. 

When  the  cercaria  is  mature  its  breaks  thru  the  wall  of  the  sporocyst  and 
swims  thru  the  surrounding  medium.  The  tail  is  retained  for  a  consider- 
able time,  and  encystment  is  slow.  This  seems  to  indicate  a  considerable 
period  of  free-swimming  Hfe. 

The  internal  structure  of  Cercaria  crenata  is  such  as  to  distinguish  it  readi- 
ly from  the  other  stylet  cercariae.  The  excretory  system  is  characterized  pos- 
teriorly by  a  subspherical  vesicle,  deeply  crenate.  It  measures  20/i  long  and 
30/i  wide.  Anterior  to  the  bladder  a  bicornuate  trunk  empties  into  the  ves- 
icle thru  a  common  median  tube.  The  horns  of  the  U  are  widely  separated. 
At  the  place  where  each  main  lateral  turns  forward  there  is  given  off  a  small 
dendritic  tubule,  directed  posteriad.     Some  distance  ahead  of  the  acetabulum 


69]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  69 

the  main  lateral  trunk  divides  into  inner  and  outer  tubes,  each  of  which  has 
a  number  of  branches  and  capillaries.  The  main  tube  of  the  tail  is  median, 
with  no  prominent  tubules. 

The  digestive  system  consists  of  an  esophagus  provided  with  a  pharynx  for 
most  of  its  way,  and,  behind  the  pharynx,  a  typical  gut  extending  to  the 
posterior  plane  of  the  acetabulum. 

The  salivary-mucin  glands  in  C.  crenata  are  of  a  unique  type.  An  outer 
series  of  eight  small  vesicular  cells,  with  a  common  duct  system  into  the  oral 
pocket,  corresponds  to  the  usual  salivary-mucin  gland  system  of  cercariae. 
These  glands  are  readily  made  out  in  the  living  worm.  An  inner  series  of 
five  cells,  two  of  which  are  just  behind  the  pharynx  and  three  behind  the  ace- 
tabulum, empty  thru  a  common  duct  system  into  the  oral  pocket.  This 
series  is  not  seen  in  the  living  larva,  but  in  stained  specimens  the  cells  show 
small  vesicular  nuclei  with  deeply  staining  cytoplasm  and  numerous  chromo- 
philic  granules.  This  inner  series  probably  consists  of  a  type  of  salivary 
gland  different  histologically  and  suggests  a  correspondingly  different  function. 

The  genital  cell  masses  are  prominent  and  are  well  differentiated  early  in 
development.  Their  structure  and  position  are  indicated  in  figure  59.  The 
ovary  lies  posterior  to  the  acetabulum  and  median  whereas  Laurer's  canal 
lies  anterior  and  to  the  left.  The  uterus  is  characterized  by  a  double  coil, 
which  ends  in  a  moderate  sized  vagina,  just  anterior  to  the  acetabulum.  The 
vitellaria  are  limited  to  three  cords  which  lie  in  a  transverse  plane  just 
posterior  to  the  ovary.  The  large  flask-shaped  testes  lie  behind  the  ovary. 
This  genital  system  suggests  the  Plagiorchiine  arrangement.  The  distribution 
of  vitellaria  is  similar  to  that  described  by  Poirier  for  Plagiorchis  sauromates 
(1886,  pi.  2). 

Cercaria  glandulosa  Faust  1917 

A  stylet  cercaria  characterized  by  a  multiplicity  of  glands  has  received 
the  name  of  Cercaria  glandulosa.  It  is  somewhat  larger  than  C.  crenata,  is 
more  oblong-ovate,  and  is  a  much  more  active  larva  (Fig.  60).  The  body 
measures  0.45  mm.  in  length  and  0.2  mm.  in  width.  The  tail  is  slightly 
shorter  than  the  body,  0.35  mm.  in  length,  by  50/i  to  60/i  in  section  at  the  base. 
The  tail  is  set  within  the  caudal  pocket.  This  pocket  is  provided  with  a 
pair  of  locomotor  grooves,  in  which  are  set  a  number  of  stiff  spines.  Below 
the  insertion  of  the  tail  is  a  small  lappet  (Fig.  63),  provided  with  three  spines 
directed  posteriad.  A  mucoid  secretion  is  present  in  the  sinuses  of  the  pocket, 
lateral  to  the  base  of  the  tail. 

The  stylet  organ  measures  39yii  in  length  by  5m  in  width  at  the  base  of  the 
shank.  It  is  reinforced  all  thru,  but  especially  at  the  base  of  the  shank,  and 
thruout  the  quill.  The  point  of  the  stylet  is  blunt.  The  stylet,  as  well  as 
the  entire  body,  is  very  delicate,  and  is  shattered  by  the  slightest  pressure  of 
the  cover  slip.  The  oral  sucker  is  directed  downward;  it  measures  86^  in 
diameter,  while  the  acetabulum,  in  the  middle  of  the  ventral  side,  is  smaller, 
with  a  diameter  of  66//. 


70  ILUNOIS  BIOLOGICAL  MONOGRAPHS  170 

The  cercaria  was  found  in  the  liver  tissues  of  Physa  gyrina  Say  from  the 
Bitter  Root  River  in  the  xdcinity  of  Hamilton,  Montana,  in  October  1916. 
Forty  per  cent  of  the  physas  examined  were  infected  with  the  parasite.  The 
cercaria  develops  within  a  very  simple  sporocyst,  which  has  a  length  of  0.34 
mm.  and  a  width  of  0.17  mm.  (Fig.  67).  The  wall  of  the  sporocyst  is  delicate, 
consisting  of  a  single  layer  of  very  thin  epidermal  ceUs,  with  no  basement  mem- 
brane and  no  muscular  complement.  The  genital  epithehum  is  localized  at  one 
end,  and  from  this  only  a  few  cercariae  are  developed  at  any  one  time. 

The  excretory  system  of  Cercaria  glandulosa  presents  some  interesting 
features.  The  bladder  is  flattened,  truncate,  and  subterminal  instead  of 
terminal.  A  narrow  canal  communicates  with  the  excretory  pore  which  is 
median  posterior.  The  four  angles  of  the  bladder  are  muscular.  When  the 
bladder  is  emptied  these  corners  lie  close  together,  so  that  the  cavity  of  the 
bladder  is  small.  Then  by  the  expansion  of  the  bladder  this  organ  is  filled 
from  the  trunks  (Figs.  64,  65).  Two  vesicular  cornua  empty  into  the  bladder. 
Each  cornu  is  directed  laterad  and  sKghtly  anteriad;  it  soon  constricts  to 
form  the  lateral  tube.  The  common  tube  divides  soon  to  form  the  posterior 
tubule  and  the  anterior  tube.  The  anterior  vessel  then  divides  in  the  region 
of  the  acetabulum  to  form  a  trifurcate  system.  Just  behind  the  region  of 
this  division  there  is  a  small  vesicular  swelling  where  granules  of  the  system 
accumulate.  The  excretory  system  in  the  tail  consists  of  the  common  medi- 
an vessel  and  several  tributaries. 

The  digestive  system  is  characterized  by  an  abundance  of  glands,  so  that 
the  entire  tract  is  surrounded  with  gland  cells.  A  small  pharynx  surrounds 
the  esophagus  near  the  anterior  end  of  the  tube.  The  esophagus  extends  to 
the  preacetabular  region,  at  which  place  it  forks  to  form  short  furcae  which 
barely  clasp  the  anterior  end  of  the  acetabulum.  Along  this  entire  course 
there  are  many  gland  cells  in  clusters,  especially  abundant  in  the  pharynx 
region.  Their  relation  to  the  pharynx  and  nerve  gangha  is  shown  in  figure  72. 
The  individual  gland  ceU  is  ovate,  with  a  short  neck.  The  cytoplasm  is 
chromophilous.  There  is  no  recognizable  duct  connection  thru  the  myoblasts 
of  the  pharynx  to  the  lumen.  The  nuclei  of  these  cells  are  large  and  studded 
with  granules. 

In  addition  to  the  grape-like  clusters  of  gland  cells  surrounding  the  entire 
digestive  tract  there  are  right  and  left  paired  gland  groups  of  the  salivary- 
mucin  type.  They  consist  of  nine  large  cells  to  each  group,  usually  situated 
in  the  acetabular  region,  but  capable  of  extension,  so  that  they  may  He  as 
far  caudad  as  the  bladder  (Fig.  62).  Figures  73  and  74  show  sections  passing 
thru  the  anterior  tip  of  the  excretory  vesicle.  In  each  of  these  a  right  and  a 
left  gland  are  visible.  In  these  glands  not  only  is  the  nucleus  granular,  but 
the  cytoplasm  is  densely  granular,  the  granules  being  assembled  in  little 
climips.  Frequently  (Fig.  73)  there  are  vacuoles  within  the  cytoplasm. 
'i%^  The  genital  organs  are  represented  by  cell  masses  which  show  clearly  the 
location  of  the  mature   organs,  but  as  yet  show  little  differentiation  (Fig. 


71]  LIFE  HISTORY  OF  TREMATODES— FAUST  71 

66).  Ovary,  Laurer's  canal,  vagina,  uterus — all  are  recognized  in  the  midace- 
tabular  region,  with  vitelline  follicles  extending  from  the  oral  aperture  to  the 
posterior  end.  They  are  divided  into  anterior  and  posterior  portions.  No 
testes  are  yet  to  be  found.  The  genital  organs  as  a  whole  seem  to  indicate 
Plagiorchid  relationship. 

Conspicuous  thruout  the  body  are  the  large  bundles  of  longitudinal  muscle 
fibers.  They  are  scattered  thruout  the  parenchyma  at  the  anterior  end 
(Fig.  72),  while  they  are  much  larger  and  more  concentrated  laterad  in  the 
region  of  the  acetabulum.  Still  further  caudad  they  become  fewer  and  less 
conspicuous  (Fig.  74). 

The  nervous  system  has  been  described  in  detail  on  page  51. 

This  cercaria  lives  a  free-swimming  existence  for  only  a  short  time.  When 
placed  in  a  watch-glass  in  tap  water,  it  soon  drops  its  tail,  preparatory  to 
encystment.  The  tail  is  helpful  in  locomotion,  yet  after  decaudation  this 
species  is  more  active  and  able  to  cover  considerably  more  ground  than  most 
other  species  v/ith  the  aid  of  the  tail.  This  movement  is  due  in  no  small 
measure  to  the  spines  in  the  locomotor  grooves  of  the  caudal  pockets.  After 
moving  about  for  a  little  while  the  cercaria  settles  down  and  pours  out  an 
abundance  of  shme  within  which  it  coils  up  and  becomes  quiescent  until  a 
transfer  to  the  new  host  is  effected. 

Cercaria  diaphana  Faust  1917 

Cerceria  diaphana  is  closely  related  to  C  glandulosa.  When  contracted, 
it  is  broadly  ovate  (Fig.  78),  but  on  extension  it  assumes  an  elongate  ovoid 
contour  (Fig.  76).  The  measurement  of  the  body  when  at  rest  is  0.2  mm.  to 
0.26  mm.  in  length  by  0.1  mm.  to  0.12  mm.  in  width.  Under  pressure  of  a 
cover  slip  the  internal  organs  are  beautifully  worked  out  and  the  delicate 
mist  of  the  parenchyma  in  which  they  are  imbedded  suggests  the  term  "dia- 
phanous. "  The  tail  is  broadly  lanceolate,  0.15  mm.  in  length  by  0.04  mm.  at 
the  base.  It  is  inserted  into  a  caudal  pocket  provided  with  spinose  locomotor 
pocket  grooves.  The  spines  are  few  in  number  (8  to  10)  and  well  developed. 
They  are  directed  meso-caudad.  As  in  C.  glandulosa  the  two  sinuses  of  the 
caudal  pocket  are  thickened  by  a  mucoid  lamination.  The  acetabulum  is 
situated  in  the  middle  of  the  ventral  side;  it  has  a  diameter  of  about  32/i.  The 
larger  and  more  powerful  oral  sucker  has  a  diameter  of  44/i.  The  stylet  organ 
(Fig.  77)  is  a  delicate  but  firm  quill  of  39/i  length  and  Sn  width  at  the  base 
of  the  shank.  It  is  entirely  without  any  reinforcement  in  the  region  of  the 
shank  but  has  thin  ventral  plates  at  the  junction  of  the  shank  and  quill,  while 
inserted  in  the  quill  point,  directed  posteriad,  is  a  minute  spine,  5/*  long  and 
0.5^1  in  diameter. 

Cercaria  diaphana  was  found  in  the  liver  tissues  of  Lymnaea  proxima  in 
the  Bitter  Root  River  near  CorvaUis  in  October  1916.  The  infection  was 
heavy.  The  cercaria  develops  in  an  oblong  sporocyst  (Fig.  79),  frequently 
drawn  out  or  contorted  at  one  end  (Fig.  80).    The  unique  feature  of  the 


72  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [72 

sporocyst  is  that  the  germinal  epithelium  is  not  localized;  consequently  germ 
balls  may  be  derived  from  any  portion  of  the  body.  Whether  or  not  the  germ 
cells  arise  parthenogenetically  has  yet  to  be  determined.  This  type  of  germ 
ball  production  represents  a  structural  simplicity  previously  not  recorded  for 
the  sporocyst. 

The  excretor\'  system  differs  from  that  of  other  stylet  cercariae  mainly 
in  the  shape  of  the  bladder  and  of  the  essential  tubes.  The  bladder  is  small, 
hea\'ily  muscular,  flattened  antero-posteriad.  Leading  out  from  it  in  a  median 
plane  is  a  non-muscular  shank  of  some  length,  which  opens  into  two  cornua 
a  considerable  distance  in  front  of  the  bladder.  Caudad  these  cornua  are 
vesicular,  but  further  cephalad  they  become  constricted  into  a  system  of 
tubules  similar  to  those  of  C.  glandulosa,  w^hich  nm  thru  the  body  to  collect 
the  excretor\'  wastes. 

The  digestive  system  consists  of  a  long  esophagus,  with  pharjTix  at  the 
anterior  end,  and  a  wide  bifurcation  somewhat  anterior  to  the  acetabulum. 
The  entire  digestive  tract  is  very  attenuate  in  outline.  It  is  not  supplied 
with  glands  along  the  furcae  but  has  an  even  more  abundant  supply 
than  C.  glandulosa  in  the  region  of  the  pharynx  (Fig.  76).  Altho  the  pharynx 
itself  measures  only  15/x  in  cross  section,  the  glandular  area  as  a  whole  em- 
braces a  sphere  65ju  in  diameter.  The  rest  of  the  tract  is  free  from  gland 
cells  of  this  nature.  The  saUvar\--mucin  glands  are  situated  in  the  upper  outer 
reaches  of  the  furcae.  Each  group  consists  of  eight  cells,  relatively  very  small, 
granular,  with  a  common  duct  system  opening  into  the  oral  pocket. 

The  genital  organs  are  similar  to  those  of  C.  glandulosa  (Fig.  78).  They 
differ  from  the  genital  cell  masses  of  that  form  in  the  more  limited  vitellaria,  and 
the  more  conspicuous  Laurer's  canal.   This  form  is  probably  a  Plagiorchid  larva. 

Unlike  C.  glandulosa  this  cercaria  is  slow  to  drop  its  tail  and  much  slower 
to  encyst,  in  spite  of  the  fact  that  there  is  an  equally  good  pair  of  posterior 
locomotor  pockets  with  spines  and  an  equally  good  supply  of  c}'stogenous. 
material.  We  have  here,  then,  e\'idence  of  a  physiological  adaptation  to 
different  conditions  of  the  en\-ironment,  where  the  structure  of  the  two  t}'pes 
would  lead  one  to  expect  similar  habits  and  reactions. 

Cercaria  dendritica  Faust  1917 

Cercaria  dendritica  is  a  species  of  cercariae  readily  recognized  by  its  obovate 
structure,  large  suckers,  large  muscular  phar\'nx,  and  large  muscular  excre- 
tor\-  vesicle.  The  body  as  a  whole  is  heavily  muscular.  The  tail  is  short 
and  almost  conical  (Fig.  81).  The  body  measures  0.33  mm.  to  0.4  mm.  in 
length  by  0.13  mm.  to  0.17  nmi.  in  wadth.  The  tail  is  about  half  the  body 
length,  0.16  mm.  and  is  0.04  mm.  wide  at  the  base.  It  is  inserted  into  a  typi- 
cal caudal  pocket,  the  whole  ca\"ity  of  which  is  lined  with  stiff  spines.  The 
large  oral  and  ventral  suckers  are  nearh'  equal  in  size.  The  former  has  a 
diameter  of  62^  and  the  latter  of  60;/.  The  stylet  (Figs.  82,  83)  is  short  and 
stout,  heavily  reinforced  at  the  shank,  with  a  flat  deltoid  quill.    The  quill 


73]  LIFE  HISTORY  OF  TREMATODES— FAUST  73 

is  pointed  at  the  tip.  It  is  directed  ventrad  by  about  ten  degrees  more 
than  the  shank.  The  stylet  has  a  length  of  44/i  and  a  breadth  at  the  base 
of  the  shank  of  14/x. 

Cercaria  dendritica  was  secured  from  two  collections  of  Lymnaea  proxima 
taken  from  the  chara  sloughs  at  Fort  Missoula,  Montana,  in  October  1916. 
The  infection  was  in  the  liver  interstices.  The  parthenita  (Figs.  87-89)  is  a 
well-developed  sporocyst,  with  an  attachment  disc,  but  without  any  indica- 
tion of  a  digestive  tract.  It  seems  to  approach  a  redia  more  nearly  in  its 
structure  than  any  other  described  sporocyst.  The  sporocyst  is  muscular  and 
heavily  covered  with  integument.  The  parthenogenetic  eggs  develop  from 
a  germinal  epithehum  situated  at  the  antipodal  end  from  the  disc.  The 
stages  of  cleavage  are  clearly  made  out  from  the  study  of  the  germ  cells  pro- 
liferating from  the  germinal  epithelium  (Fig.  89).  This  layer  is  closely 
pressed  against  the  epidermis.  As  the  cells  mature  they  increase  in  size. 
The  increase  continues  thruout  the  cleavage,  so  that  a  three-cell  stage  is 
larger  than  a  one-cell  stage,  and  a  morula  is  larger  than  a  five-cell  stage.  This 
continued  growth  of  the  embryo  is  accounted  for  by  the  nourishing  medium 
which  bathes  the  sporocyst.  This  is  a  special  case  of  nurture,  where  the 
growth  stimulus  is  reacted  to  immediately.  The  germ  ball  attains  a  con- 
siderable size  before  it  begins  to  differentiate,  altho  epiboly  has  occurred  soon 
after  the  morula  stage  has  been  reached.  The  animal  is  mature  before  it 
breaks  thru  the  wall  of  the  sporocyst  and  swims  out  into  the  inter-cecal  spaces. 

The  larva  has  an  interesting  excretory  system  (Fig.  81).  An  immense 
spheroid  bladder,  somewhat  crenate,  opens  dorso-posteriad  thru  a  small  pore. 
Anterior  it  receives  the  contents  of  two  large  muscular  comua  thru  a  common 
opening.  These  cornua  extend  laterad  to  the  extreme  margin  of  the  animal. 
At  the  outside  of  each,  at  the  margin  of  the  worm,  arise  three  tubes,  one 
directed  posteriad  and  two  directed  anteriad.  The  capillaries  are  dendritic. 
The  caudal  tube  is  a  median  canal  without  any  prominent  tubules. 

The  alimentary  system  consists  of  a  pharynx  with  muscular  fibers  developed 
early.  It  has  a  width  of  30^  and  a  length  in  section  of  36ijl.  A  short,  attenuate 
esophagus  opens  posteriad  into  two  vestigial  furcae.  Anterior  and  lateral 
to  the  acetabulum  are  the  salivary-mucin  glands,  eight  to  each  group.  They 
are  moderately  large  (Fig.  85),  and  empty  thru  common  duct  systems  into 
the  oral  pocket. 

The  conspicuous  features  of  the  genital  system  (Fig.  86)  are  the  large  swollen 
vagina,  and  the  prominent  Laurer's  canal,  the  latter  extending  out  on  the 
left  side  of  the  acetabulum  under  its  posterior  margin.  In  the  mid-area, 
just  behind  the  acetabulum,  are  two  small  pyriform  testes.  The  vitelline 
glands  extend  from  the  extreme  anterior  margin  of  the  worm  to  the  extreme 
posterior  end;  they  are  attenuate,  sparsely  branching  serpentine  chords, 
composed  of  a  long  anterior  and  a  short  posterior  portion.  The  vitelline 
ducts  run  in  from  the  postero-lateral  regions  to  the  ootype,  which  is  just 
anterior  to  the  testes.    This  type  is  suggestive  of  Plagiorchid  relationships. 


74  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [74 

Soon  after  the  cercaria  is  set  free  into  the  water,  it  drops  its  tail.  Ahnost 
before  the  observer  is  aware  it  secretes  a  thin  membrane  from  the  abundance 
of  cystogenous  material  contained  in  the  large  cyst  cells  which  pack  the  paren- 
chyma of  the  worm.  The  oval  c>'st  with  the  worm  coiled  up  inside  is  shown 
in  figure  84.  This  type  of  cyst  offers  only  a  temporary  lodgement  for  the 
cercaria,  and  it  is  evident  that  the  worm  must  reach  the  definitive  host  soon 
if  the  infection  is'  to  be  successful. 

Cercaria  micropJiarynx  Faust  1917 

Cercaria  micropJiarynx  is  a  minute  larva  of  the  xiphidiocercariae,  oval  in 
contour,  with  small  clavate  tail  (Fig.  93).  The  body  is  covered  with  minute 
spines  arranged  in  diamond  pattern,  progressively  less  prominent  toward 
the  caudal  end.  The  spines  are  probably  constant  characters  of  the  adult 
as  weU  as  of  the  larva,  since  the  entire  trunk  is  well  suppHed  with  these  spines 
while  the  tail  is  naked.  The  body  measures  0.18  mm.  in  length  and  0.09  mm. 
in  width.  The  tail  is  0.14  mm.  long  and  0.03  mm.  at  the  base.  It  is  inserted 
into  a  caudal  pocket  provided  with  a  group  of  spines  on  the  lateral  lappets 
ventral  to  the  tail.  The  oral  sucker  is  large  for  the  bod}'-  size,  35^1  in  diameter, 
while  the  acetabulum  is  shghtly  smaller,  30/i  in  diameter.  Inserted  in  the 
hood  of  the  oral  sucker  is  the  stylet  organ  (Figs.  91,  92),  34fi  long  and  5n  to 
6fi  in  breadth  along  the  shaft.  The  organ  is  reinforced  all  around  and  has  a 
velum  stretched  across  the  ventral  surface  of  the  quiU. 

The  cercaria  was  secured  from  the  infected  Uver  tissues  of  a  large  number 
of  Lymnnea  proxima,  taken  from  Rattlesnake  Creek,  Missoula,  in  Novem- 
ber 1916  and  in  May  1917.  The  cercariae  develop  in  oval  irregular  sporo- 
cysts,  measuring  0.24  mm.  along  the  long  axis  and  0.18  mm.  along  the  short 
axis  (Fig.  94).  The  body  wall  of  the  sporocyst  consists  of  a  single  layer  of 
epidermal  cells,  between  which  are  found  numerous  excretory  granules,  lying 
in  irregular  grooved  channels.  There  is  no  localization  of  the  germinal  epi- 
theUum,  so  that  germ  balls  arise  from  aU  portions  of  the  body  wall  and,  when 
mature,  break  out  into  the  body  lumen.  Not  only  do  the  cercariae  develop 
to  maturity  in  the  sporocyst,  but  in  some  cases  they  drop  their  tails  and 
encyst  in  the  sporocyst  (Fig.  95).  Thus  the  larval  host,  the  snail,  is  the  food 
of  the  intercalated  or  of  the  definitive  host,  since  no  free-living  stage  is  com- 
monly found.  In  case  the  cercaria  is  pressed  out  of  the  sporocyst  before 
encystment,  it  swims  about  for  a  very  brief  period,  then  drops  the  tail  and 
enc>^sts. 

The  excretory  system  consists  of  a  subspherical  vesicle  and  bellows-shaped 
comua,  which  open  into  the  vesicle  thru  a  common  cylinder.  The  three 
usual  tubes  of  the  excretory  system  are  present,  the  single  posterior  and  the 
two  anterior  ones.  The  tail  tube  is  single  median,  with  a  few  inconspicuous 
lateral  tributaries.  The  comua  are  filled  with  excretory  fluids;  they  are 
Imed  with  cells  (Fig.  98). 

The  digestive  system  consists  of  the  very  minute  pharynx  in  the  mid- 
region  of  the  esophagus,  and  two  vesicular  f urcae  considerably  anterior  to  the 


75]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  75 

acetabulum.  No  glands  occur  in  the  pharynx  or  cecal  regions,  but  in  the 
prepharynx  region,  just  within  the  oral  aperture,  is  a  band  of  about  fifty  gob- 
let cells  of  a  glandular  nature.  The  salivary-mucin  glands  are  found  at  the 
sides  of  the  acetabulum.  They  consist  of  eight  cells  for  each  group.  They 
are  relatively  large,  vesicular,  and  have  common  ducts  opening  into  the  oral 
pocket.  In  addition  to  the  usual  transverse  and  longitudinal  systems  just 
within  the  integument  (Fig.  97,  98),  large  muscle  elements  are  scattered 
thruout  the  parenchyma. 

The  genital  organs  (Fig.  96)  consist  of  a  prominent  vagina,  a  well-defined 
Laurer's  canal,  and  a  group  of  massed  organs  in  the  vicinity  of  the  ootype. 
In  addition,  there  are  the  yolk  follicles,  distributed  over  a  wide  range  of  the 
dorsal  side  of  the  animal.  The  follicles  are  closely  massed  together.  This 
species  suggests  a  Plagiorchid  genital  system. 

Cercaria  racemosa  Faust  1917 

Cercaria  racemosa  belongs  to  that  group  of  stylet  cercariae  usually  desig- 
nated as  cercariae  ornatae,  by  virtue  of  their  possession  of  a  fin-fold  structure 
to  the  tail.  While  this  separation  may  be  concomitant  with  a  deeper,  more 
fundamental  difference  of  type,  it  is  well  to  bear  in  mind  that  fin-folds  occur 
in  other  groups,  such  as  in  monostomes,  Cercaria  lophocerca  (Fihppi,  1857:5; 
Fig.  3),  echinostomes,  Cercaria  echinatoides  Fil.  (La  Valette:1855,Taf.  I,  C), 
and  among  the  furcocercous  larvae,  Cercaria  cristata  (La  Valette,  1855,Taf. 
II,  K).  It  may  be  looked  on  as  a  modification  of  the  caudal  organ  for  swim- 
ming. 

The  body  of  Cercaria  racemosa  is  elongate  ovoid,  measuring  0.29  mm.  in 
length  by  0.11  mm.  in  width  (Fig.  100).  It  is  characteristically  broadest 
just  ahead  of  the  acetabulum.  The  tail  consists  of  a  central  lanceolate  region 
and  a  lateral  ruffled  fringe,  which  is  most  conspicuous  at  the  distal  end.  The 
tail  measures  0.22  mm.  in  length  and  0.04  mm.  in  width  at  the  base.  It  is 
inserted  into  the  posterior  extremity  of  the  trunk,  altho  there  are  no  lateral 
sinuses  to  be  found  in  this  caudal  pocket.  The  acetabulum  is  sHghtly  caudal 
to  the  middle  of  the  body.  It  measures  26/i  in  diameter,  while  the  larger  oral 
sucker  has  a  diameter  of  36iu.  The  stylet  organ  (Figs.  101,  102)  is  delicately 
attenuate,  with  a  reinforced  tip.     It  is  27/i  long  and  about  5^  wide  at  the  base. 

The  species  was  found  in  the  liver  of  Lymnaea  proxima  in  the  chara  sloughs 
of  the  Bitter  Root  River  at  Fort  Missoula,  Montana,  in  October  1916.  It 
occurred  as  a  minor  infection  along  with  C.  dendritica  and  C.  gracillima.  The 
parthenita  is  an  irregular  polygonal  sporocyst  about  0.62  mm.  long  and  0.38 
mm.  thick  (Figs.  104,  105).  At  one  end  is  situated  a  pocket  of  glandular 
cells  which  attach  the  sporocyst  to  the  host.  This  is  done  by  the  exudation 
of  a  mucus.  It  is  doubtful  if  these  cells  are  at  all  muscular.  At  the  antipodal 
end  is  the  germinal  epithehum,  from  which  germ  balls  arise.  Only  a  few 
cercariae  develop  within  the  sporocyst  at  any  one  time. 

The  bladder  of  the  excretory  system  is  truncate,  with  a  common  median 
vessel  leading  into  it  from  the  anterior  end.    Lining  the  vesicle  at  the  anterior 


76  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [76 

end  are  six  gland  cells,  paired  right  and  left.  They  appear  as  small  tubercules 
suspended  from  the  anterior  wall  of  the  vesicle.  Anterior  to  the  median  vessel 
are  two  cornua,  elongate,  yet  swollen,  reaching  antero-laterad  around  the 
acetabulum.  Near  the  acetabulum  there  are  received  the  common  posterior 
and  the  two  anterior  tubules.  The  pattern  of  the  capillaries  is  racemose. 
The  tail  trunk  system  consists  of  a  common  median  vessel  with  many  lateral 
tubules.    The  entire  system  is  filled  with  minute  excretory  granules. 

The  digestive  system  consists  of  a  very  long  esophagus,  near  the  anterior 
end  of  which  is  the  small  sphincter,  and  from  the  posterior  end  of  which  the 
furcae  arise.  They  extend  partly  around  the  acetabulum.  The  salivary-mucin 
glands  consist  of  right  and  left  paired  groups  of  cells,  eight  to  the  group,  with 
long  ducts  leading  in  a  common  bundle  to  the  oral  pocket. 

In  the  region  of  the  cerebral  ganglion  a  pair  of  oval  bodies,  the  non-pig- 
mented  eye-spots  are  located.  They  are  degenerate,  similar  to  those  eyes 
described  for  Cercaria  gracillima  (p.  52). 

The  genital  cell  masses  are  found  in  the  region  of  the  acetabulum  (Figs. 
104,  107).  To  the  left  is  Laurer's  canal,  and  running  dextro-laterad  is  the 
closely  coiled  uterus.  The  genital  pore  is  on  the  right  of  the  mid-ventral  line, 
anterior  to  the  acetabulum.  Running  into  the  ootype  from  the  postero- 
lateral angles  are  the  vitelline  ducts,  connecting  the  vitellaria  with  the  ootj'pe. 
The  testes  are  not  well  defined.  The  relationship  of  the  cercaria  is  not  evi- 
dent from  the  genital  cell  masses. 

Cystogenous  cell  glands  are  present,  altho  not  as  conspicuous  as  in  C. 
glandulosa  or  C.  micro  pharynx.  Encystment  takes  place  after  a  considerable 
period  of  free  swimming  life.  Decaudation  always  precedes  encystment. 
The  cyst  wall  is  thin ;  the  animal  is  easily  viewed  thru  the  cyst. 

Echinostome  Cercariae 
Cercaria  trisolenata  Faust  1917 

Cercaria  trisolenata  represents  a  unique  type  of  echinostome  larva  (Fig. 
109).  It  is  more  attenuate  than  the  average  species  of  this  family,  and  has 
an  unusually  short  tail.  The  body  has  an  average  length  of  0.45  mm.  and  a 
width  at  the  preacetabular  region  of  0  1  mm.  The  tail  is  about  0.2  mm.  long, 
lanceolate,  and  measures  0.06  mm.  at  the  base.  An  anterior  region  of  the 
trunk,  measuring  0.06  mm.  along  the  median  line,  constitutes  the  head  region, 
behind  which  is  a  neck-like  constriction.  There  is  a  collar  of  36  spines  along 
the  margin  of  the  head,  arranged  in  a  single  irregular  series  (Figs.  110,  111). 
These  spines  are  bluntly  rounded  at  the  base  and  taper  to  a  rounded  point 
at  the  distal  end.  They  are  from  12/x  to  14jLt  in  length.  The  body  as  a  whole 
is  usually  covered  with  minute  spines.  The  acetabulum  is  beset  with  an 
irregular  arrangement  of  crooked  spines  (Fig.  112).  The  oral  sucker  is  small 
but  powerful,  Z^ti  in  diameter.  The  acetabulum,  situated  behind  the  mid- 
plane  of  the  body,  measures  42)u. 

These  cercariae,  together  with  Cercaria  gracillima,  are  the  most  cosmopoli- 
tan species  of  the  Bitter  Root  River.     They  occur  in  Physa  gyrina  from  the 


77]  LIFE  HISTORY  OF  TREMATODES— FAUST  77 

upper  and  lower  reaches  of  the  Valley,  and  in  Planorbis  trivolvis  from  the  region 
of  Buckhouse  Bridge.  The  infection  of  the  host  is  always  heavy,  both 
as  relates  to  numbers  of  individuals  infected  and  the  number  of  parasites  in 
the  individual  host.  The  per  cent  of  infection  ranges  from  22  to  100.  The 
parasite  is  located  primarily  in  the  interstices  of  the  liver,  but  frequently 
invades  the  cecal  walls  and  does  great  injury  to  the  tissues. 

The  cercaria  develops  in  a  redia  of  well-marked  characters  (Fig.  117). 
The  redia  measures  about  1.0  mm.  in  length  and  has  a  mid-diameter  of  0.22 
mm.  and  a  gross  width  of  0.35  mm.  across  the  region  of  the  locomotor  feet. 
A  small  powerful  pharynx  at  the  anterior  end  opens  into  the  rhabdocoel  gut 
which  fills  the  greater  part  of  the  body  cavity,  extending  almost  to  the  posterior 
extremity.  The  germinal  epithehum  is  at  the  posterior  end.  From  this 
layer  the  ova  develop,  which  grow  into  cercariae.  The  first  character  of  the 
germ  ball  to  become  diflferentiated  superficially  is  the  oral  sucker  (see  series 
of  stages  in  figure  114),  Later  the  tail  and  the  acetabulum  become  marked 
off,  and  finally  the  oral  hood. 

At  the  posterior  end  a  small,  non-muscular,  truncate  bladder  is  situated. 
It  opens  anteriad  into  two  simple  unbranched  tubes.  These  can  be  traced 
cephalad  inside  the  intestinal  ceca  to  the  head  of  the  worm.  The  cephalic 
end  of  the  excretory  system  is  unique.  Lateral  to  the  pharynx,  a  triangular 
channel-system  is  found.  From  the  anterior  angle  a  small  capillary  leads 
forward  to  a  single  flame  cell.  From  each  of  the  other  two  angles  a  small 
capillary  leads  back  to  a  flame  cell.  This  constitutes  the  trisolenate  sys- 
tem at  the  anterior  terminus  of  the  excretory  tract.  The  tail  excretory  tube 
is  a  single  median  structure  and  has  no  laterals  or  terminal  outlet.  This 
fact  necessitates  a  revision  of  the  scheme  proposed  by  Cort  (1915:37),  in 
which  this  writer  characterizes  the  excretory  system  of  echinostome  cercariae 
as  "opening  on  each  side  of  the  anterior  part  of  the  tail. "  It  seems  from  the 
present  investigation  that  the  three  flame  cells  in  the  anterior  part  of  the 
trunk  may  be  a  more  reasonable  criterion  for  distinguishing  the  excretory 
system  of  this  group.  Further  work  on  other  forms  must  be  done  before  this 
can  be  definitely  proposed. 

Excretory  granules  fill  the  lateral  excretory  trunks  from  the  pharynx 
region  as  far  caudad  as  the  acetabulum. 

The  digestive  system  is  simple.  It  consists  of  a  long  esophagus,  with  a 
very  small  pharynx  sphincter  about  in  its  middle,  and  two  very  long  furcae, 
extending  to  the  sub-caudal  region. 

The  genital  cell  masses  are  yet  very  immature.  There  are  four  cell  masses 
present,  one  on  the  upper  right  of  the  acetabulum  (Fig.  130),  the  vagina;  one^ 
behind  the  acetabulum  (Fig.  131),  the  ovary,  and  two  tandem  masses  in  front 
of  the  bladder  (Fig.  120),  the  testes.  In  the  vicinity  of  the  ovary  are  num- 
erous viteUine  follicles,  but  they  have  not  been  found  to  follow  any  definite 
pattern. 


78  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [78 

The  nervous  system  of  this  species  has  been  made  the  basis  of  the  dis- 
cussion on  page  49,  and  needs  no  further  consideration  here. 

The  musculature  is  ahnost  all  parietal,  except  for  the  walls  of  the  intestinal 
tract.  Parietal  and  splanchnic  muscles  are  similar  in  structure.  The  former 
consist  of  external  transverse  and  internal  longitudinal  bundles,  while  the 
latter  consist  of  external  longitudinal  and  internal  transverse  fibers  (Figs. 
118,  119).  Each  fiber  can  be  traced  to  a  myoblast,  the  central  figure  of  which 
is  the  large  oval  nucleus,  with  karyosome  and  radiating  processes,  so  that 
the  whole  figure  appears  stellate.  There  are  several  fibers  originating  from 
each  myoblast;  they  always  nm  along  a  single  axis.  The  longitudinal  mus- 
cles of  the  tail  are  prominent  (Fig.  133). 

The  body  is  filled  with  a  parenchyma  complex,  consisting  of  undifferen- 
tiated cells,  connective  tissue  fibers,  and  cystogenous  gland  cells.  In  the  tail 
of  an  immature  cercaria  (Fig.  133),  there  is  a  partition  of  parenchyma  cells, 
separating  the  caudal  excretory  canals  into  right  and  left  tubules.  This 
condition  disappears  as  the  animal  matures,  altho  vestiges  of  these  cells  may 
be  found  in  the  mature  cercaria. 

The  cystogenous  cells  are  differentiated  parenchyma  cells,  filled  with  a 
mucoid  in  the  form  of  oval  granules.  In  the  ordinary  cystogenous  cell  (Fig. 
113),  the  granules  are  about  l/i  by  0.6/i  in  section.  There  is  a  central  nucleus 
to  each  of  these  cells,  with  poorly  defined  membrane  separating  it  from  the 
cytoplasm.  It  is  conspicuous  because  of  its  large  number  of  chromatic  gran- 
ules, composed  of  elongate  flecks.  These  flecks  are  also  present  in  considerable 
numbers  thruout  the  cytoplasm;  they  are  especially  massed  against  the  cell 
walls.  The  glands  are  best  developed  in  the  middle  of  the  body  (Fig,  109, 
sections  hb  and  dd).  Since  the  cystogenous  glands  are  well  developed,  the 
cyst  wall  is  heavy  (Fig.  115,  A-C).  In  crawling  over  the  surface  of  any  object 
the  mature  cercaria  squeezes  off  the  tail  by  a  constriction  of  the  posterior 
transverse  muscles.  A  final  jerk  of  the  tail  frees  it  from  the  body.  Immedi- 
ately the  cystogenous  glands  pour  out  a  mucus  aroimd  the  contracting  worm, 
so  that  at  first  an  oval  cyst  is  formed.  Later,  as  it  hardens,  it  assumes  a  more 
spherical  outline  (Fig.  116).  Thru  this  cyst  membrane  the  excretory  and 
digestive  systems  of  the  body  and  the  collar  spines  are  readily  distinguished. 
The  cysts  are  so  well  walled  and  so  numerous  that  they  suggest  a  considerable 
period  of  wintering  over. 

Cercaria  biflexa  Faust  1917 

Cercaria  biflexa  belongs  to  a  type  of  echinostome  cercariae  distinguished 
by  a  smooth  body  outline,  a  long  powerful  taU,  blunt  oral  hood  spines  and  a 
reflexed  excretory  tube.  The  excretory  system  worked  out  by  Looss  (1894: 
Fig.  191c)  for  Distomum  echinatum  approaches  the  system  in  this  species  to 
some  extent,  but  differs  from  it  in  many  details. 

The  body  of  Cercaria  biflexa  is  elongate  ovoid,  with  a  slight  constriction 
just  behind  the  oral  hood  (Figs.  134,  135).  Both  the  body  and  the  tail  are 
extraordinarily  muscular.    The  body  measures  0.45  mm.  to  0.5  mm.  in  length 


79]  UFE  HISTORY  OF  T REM ATODES— FAUST  79 

and  0.13  mm.  to  0.15  mm.  in  width.  The  tail  is  at  least  as  long  as  the  body 
or  slightly  longer.  Its  width  is  about  0.05  mm.  at  the  base.  The  oral  sucker 
has  a  diameter  of  55At  and  the  ventral  sucker,  situated  at  the  beginning  of  the 
posterior  third  of  the  body,  measures  65/*  in  diameter.  Around  the  oral  hood 
is  a  circlet  of  collar  spines,  42  in  number,  ovoid  elongate,  bluntly  rounded  at 
both  ends,  with  a  length  of  10/t  to  15/1  and  a  thickness  of  3/i. 

The  worm  was  found  in  Physa  gyrina  in  November  1916,  and  in  Planorhis 
trivolvis  in  May  1917,  in  the  neighborhood  of  Buckhouse  Bridge,  near 
Fort  Missoula,  Montana. 

The  parthenita  is  a  redia  with  a  length  measurement  of  0.4  mm.  and  a 
thickness  of  0.088  mm.  (Fig.  137).  The  locomotor  feet  are  short,  blunt  pro- 
cesses in  the  posterior  third  of  the  body,  and  have  a  gross  span  of  0.1  mm. 
In  contrast  to  the  large  gut-pouch  of  Cercaria  trisolenata  parthenitae,  the 
rediae  of  this  species  have  short  inconspicuous  rhabdocoel  guts,  only  0.1  mm. 
in  length.  One-third  of  this  is  occupied  by  the  pharynx.  The  body  wall 
is  covered  with  a  thick  integument,  within  which  is  a  heavy  muscular  layer. 
At  the  posterior  end  are  a  number  of  small  spinous  projections  (Fig.  141). 
The  germinal  epithelium  also  is  at  the  posterior  end.  A  noticeable  feature 
of  the  cleaving  ova  is  their  flattened  condition  (Fig.  141).  Stages  in  matura- 
tion and  cleavage  are  seen  in  this  figure  and  may  be  compared  with  similar 
stages  of  maturation  and  development  in  C.  trisolenata  (Fig.  140.)  The  cer- 
cariae,  when  mature,  escape  thru  the  birth-pore  situated  ventrolaterad. 

A  prominent  excretory  system  is  foimd  in  this  cercaria  (Fig.  135).  The 
vesicle  is  a  cylindrical  organ  inflated  posteriorly.  It  is  not  muscular  to  any 
marked  degree.  Tubular  cornua  empty  into  the  anterior  end  of  the  bladder. 
As  these  cornua  are  traced  forward  lateral  tributaries  are  found  to  empty 
into  them  at  regular  intervals.  In  the  region  of  the  pharynx  the  tubes  become 
attenuated  and  bend  twice  upon  themselves  (Fig.  138) .  The  detailed  descrip- 
tion of  this  anterior  end  of  the  system  of  Cercaria  biflexa  is  found  in  the  section 
on  morphology  (p.  40).  It  may  be  noted  here  that  there  are  three  flame  cells 
along  the  course  of  the  ultimate  tubule  of  the  system,  and  that  these  seem 
comparable  to  the  three  flame  cells  found  in  C.  trisolenata.  The  excretory 
tube  in  the  tail  is  a  single  median  tube  for  about  two-fifths  of  the  way  distad, 
at  which  point  it  forks  and  continues  double  the  remainder  of  the  way  distad, 
with  numerous  cross-anastomoses.  It  does  not  open  to  the  outside  either 
on  the  sides  or  end. 

The  digestive  system  consists  of  an  extremely  long  esophagus,  extending 
all  the  way  to  the  acetabulum;  furcae  which  end  at  the  caudal  end  of  the 
animal;  and  salivary-mucin  glands,  developed  to  a  very  high  degree.  These 
latter  consist  of  an  inner  and  an  outer  series  of  right  and  left  groups  (Fig.  134). 
There  are  from  fifty  to  sixty  cells  in  each  group,  in  oblong  clusters,  with  a 
common  duct  anterior  to  each  series  leading  cephalad.  The  two  ducts  of  each 
side  fuse  to  form  a  single  lateral  duct  which  leads  into  the  oral  pocket.  These 
glands  are  different  from  the  majority  of  mucin  glands  in  being  differentiated 


80  ILUNOIS  BIOLOGICAL  MONOGRAPHS  ^ 

into  inner  and  outer  series.  The  condition  is  similar  in  part  to  that  in  Cer- 
carta  crenaia  (Fig.  55),  in  which  species  there  is  also  a  double  series  of  glands 
on  each  side  of  the  esophagus.  But  in  this  case  the  glands  of  the  inner  and 
outer  series  are  not  different  in  structure  and  function  as  in  C.  crenata.  Here, 
too,  the  ducts  are  not  composed  of  a  bundle  of  separate  ducts,  as  is  found  in 
C.  marcianae  (La  Rue,  1917:5),  but  consist  of  a  single  common  duct  for  the 
entire  group  of  gland  cells. 

The  genital  system  is  much  further  developed  in  this  species  than  in  C. 
trisolenata  (Fig.  139).  Behind  the  acetabulum  is  the  ovary,  from  which  a 
uterus  leads  around  the  acetabulum,  ending  in  a  swollen  vagina  in  the  pre- 
acetabular  region.  Only  the  transverse  ducts  of  the  vitelline  system  are 
differentiated.  Behind  these  are  the  two  testes,  unequal  in  size,  one  above 
the  other. 

The  encystment  of  Cercaria  biflexa  is  similar  to  that  of  C.  trisolenata  in 
that  it  depends  on  the  secretion  of  mucoids  from  a  large  number  of  cystogenous 
glands  in  the  parenchyma.  It  differs,  however,  in  the  two  species  both  as  to  time 
and  place  of  encystment.  Cercaria  trisolenata  encysts  only  after  it  has  escaped 
from  the  liver  tissues  of  the  host.  C.  biflexa  encysts  within  the  host,  immedi- 
ately upon  breaking  thru  the  birth-pore  of  the  redia.  Thus  a  section  of 
Planorbis  trivolvis  liver  tissue  shows  the  interstices  of  the  Hver  ceca  filled  with 
encysted  cercariae,  which  continue  to  grow  and  differentiate  within  the  pri- 
mary host  (Fig.  159). 

Furcocercariae 
Cercaria  graciUima  Faust  1917 

Cercaria  graciUima  is  a  furcocercous  cercaria  more  slender  than  those 
previously  described.  This  species,  together  with  C.  tuberistoma  (p.  82), 
constitute  the  second  instance  of  furcocercous  cercariae  to  be  described  for 
North  America,  the  first  being  C.  douthiUi  Cort  (1915:50-52;  Figs.  55-64). 
In  addition  to  the  forked-tail  character  of  these  three  species,  they  lack  a 
pharynx,  and  have  paired  salivary-mucin  glands  leading  into  the  oral  pocket, 
composed  of  four  or  more  cells  to  each  group.  The  "eyelet"  excretor>'  ana- 
stomosis, connecting  the  excretory  system  of  the  body  and  the  tail  is  also  a 
common  character. 

Cercaria  graciUima  has  an  oblong  cylindrical  body  (Fig.  142).  The 
branched  portion  of  the  tail  is  elongate  lanceolate.  The  body  length  varies 
from  0.13  mm.  to  0.16  mm.  and  the  diameter  of  the  worm  varies  from  0.02 
mm.  to  0.03  mm.  The  unbranched  portion  of  the  tail  is  about  0.16  mm.  long 
and  the  caudal  rami  are  of  equal  length.  The  former  is  0.02  mm.  to  0.03  mm. 
in  diameter  and  the  ramus  has  a  width  of  0.01  mm.  The  trunk  is  characterized 
further  by  the  absence  of  a  true  oral  disc,  while  in  its  place  there  is  an  invertible 
sucker.  A  ventral  sucker,  12fi  in  diameter,  varies  in  location,  according  to 
the  movements  of  the  animal,  from  the  middle  of  the  ventral  side  to  a  position 
considerably  farther  forward.  The  cephalic  region  is  ovately  rounded  when 
the  sucker  is  fully  distended  and  is  crowned  by  a  cap  of  small  spines.    A 


81]  LIFE  HISTORY  OF  TREMATODES— FAUST  81 

feature  of  this  cercaria,  in  common  with  that  of  C.  douthitti,  is  the  possession 
of  eye-spots  (Figs.  144,  150).  But  the  eye-spots  of  C.  gracillima  are  the  more 
vestigial,  for  they  have  no  pigment. 

This  species  was  found  in  the  livers  of  Fhysa  gyrina  Say,  collected  from 
the  lower  reaches  of  the  Bitter  Root  River  near  Maclay  Bridge,  Buckhouse 
Bridge,  and  the  sloughs  at  the  Roadhouse,  near  Fort  Missoula,  in  the  fall  of 
1916.  In  addition  it  was  found  in  the  livers  of  Lymnaea  proxima  Lea  from 
Rattlesnake  Creek,  Missoula.  The  infection  in  most  cases  was  not  exceed- 
ingly heavy,  except  in  the  collection  from  the  sloughs  at  the  Roadhouse, 
where  thirty-three  out  of  seventy-one  individuals  were  infected,  or  46.5  per 
cent. 

The  cercariae  develop  in  long  cylindrical  sporocysts,  varying  in  length 
from  0.25  mm.  to  0.1  mm.,  but  most  frequently  averaging  about  0.5  mm. 
(Figs.  146,  147).  In  diameter  the  sporocysts  vary  from  0.2  mm.  to  0.4  mm. 
The  parthenita  is  a  simple  structure,  non-muscular,  depending  on  the  daughter 
cercariae  for  its  movement.  At  one  end  (Fig.  147)  is  a  non-muscular  attach- 
ment area;  at  the  other  end,  merely  a  rounded  non-differentiated  cap.  The 
germinal  epithehum  is  localized  at  the  attachment  end.  From  this  mass  the 
daughter  worms  develop.  Internal  pressure  from  the  developing  larvae 
increases  the  length  and  diameter  of  the  parthenita.  In  development  (Fig, 
148),  the  ovoid  germ  ball  first  differentiates  a  tail  portion;  later  the  rami 
appear.  It  is  not  until  considerably  later  that  the  acetabulum  is  found.  The 
oral  spines  appear  only  when  the  larva  is  mature. 

The  movement  of  the  cercaria  is  characteristic  for  furcocercariae.  The 
main  movement  consists  in  a  very  strenuous  beating  and  lashing  of  the  rami, 
so  that  the  head  is  pushed  into  the  object  with  which  it  comes  in  contact. 
In  case  the  head  is  not  forced  into  the  object,  the  worm  is  set  free  by  a  back- 
ward movement  of  the  tail  and  the  entire  worm  squirms  around  until  it  comes 
in  contact  with  another  object,  when  the  same  boring  movement  is  again 
attempted.  The  oral  end  of  the  cercaria  is  much  better  adapted  to  this  type 
of  invasion  of  the  tissues  to  be  infected  than  if  it  possessed  an  oral  disc. 

The  excretory  system  of  C.  gracillima  is  embryologically  a  single  paired 
system  for  both  body  and  tail.  As  development  and  differentiation  of  parts 
progress  the  tubes  in  the  posterior  extremity  of  the  trunk  and  the  anterior 
region  of  the  tail  fuse,  to  form  a  median  bladder  and  the  common  tube  of  the 
proximal  region  of  the  tail.  There  remains  the  bifurcated  portion  in  the 
laterals  of  the  trunk  and  the  rami  of  the  tail,  and  in  addition,  the  "eyelet 
anastomosis."  This  eyelet  structure  has  been  observed  by  Looss  (1896:172- 
174;  PL  15),  m  Cercaria  vivax  Sons,  and  by  Cort  (1915,  Fig.  57)  in  C.  douthitti. 

The  excretory  system  in  the  body  consists  of  two  lateral  tubes  that  diverge 
from  the  bladder  and  can  be  traced  forward,  together  with  dendritic  tubules 
and  capillaries,  the  internal  ones  of  which  frequently  form  chiasmic  anasto- 
moses across  the  median  plane  of  the  body.  Slightly  posterior  to  the  middle 
of  the  body  the  lateral  tube  expands  and  opens  into  a  pocket  provided  with 


82  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [82 

dlia  (Fig.  145).  These  cilia  come  from  a  flame  cell  bordering  on  the  lumen 
of  the  lateral  tube.  A  second  pocket  somewhat  anterior  is  an  atrium  into  which 
many  of  the  capillaries  empty;  it  is  filled  with  small  excretory  granules,  in 
this  way  acting  as  a  secondary  reservoir. 

The  digestive  system  of  C.  gracillima  consists  of  an  unbranched  esophagus 
without  a  pharynx  sphincter,  a  pair  of  short  degenerate  furcae  extending 
posteriad  beyond  the  acetabulum,  and  a  ring  of  gland  cells  in  the  region  of  the 
esophagus  where  the  pharynx  might  be  expected.  Opening  into  the  oral 
atrium  thru  common  bundles  of  ducts  are  the  salivary-mucin  glands  (Fig.  144). 
These  glands  are  very  large  with  vesicular  nuclei.  They  are  situated  in  the 
posterior  third  of  the  body.  In  cross  section  the  ducts  are  similar  to  those 
described  by  Cort  (1915,  Figs.  59-62)  for  C.  douthUti. 

The  nervous  system  has  been  discussed  on  page  54. 

The  genital  cell  masses  in  the  cercaria  are  hermaphroditic  (Fig.  149). 
Anterior  to  the  acetabulum  are  the  vagina  and  the  cirrus  pouch  buds,  and 
lateral,  extending  both  anteriad  and  posteriad,  are  the  viteUine  foUicles.  In 
the  posterior  extremity  is  a  conical  germinal  mass,  from  which  are  proliferated 
anteriad  a  number  of  small  testicular  folMcles. 

The  general  features  of  this  fluke  make  it  possible  to  refer  it  to  the  Schis- 
tosomatidae. 

Cercaria  tuberistoma  Faust  1917 

This  species  of  cercaria  is  shorter  and  much  more  muscular  than  C.  gracil- 
lima. The  body  is  elongate  ovoid,  with  the  anterior  end  slightly  constricted 
and  crowned  with  a  pair  of  tuberosities  (Fig.  155).  The  body  length  is  about 
0.2  mm.  and  the  width  0.05  mm.  to  0.06  mm.  The  tail  measures  about  0.32 
mm.  as  a  whole,  equally  divided  into  common  portion  and  rami.  There  is 
no  oral  suctorial  disc,  but  instead  the  oral  invertible  proboscis.  The  acetabulum 
measures  0.03  mm.  in  diameter. 

The  cercaria  was  secured  from  a  single  Ught  infection  of  Physa  gyrina 
collected  in  the  Bitter  Root  River  at  Corvallis,  Montana,  in  October  1916. 
Out  of  nineteen  snails  examined  only  one  was  infected.  Only  a  few  cercariae 
were  secured,  and  these  were  studied  as  Hve  mounts.  From  this  study  the 
excretory,  digestive  and  general  body  features  were  worked  out. 

The  cercaria  develops  in  an  elongate,  dumb-bell-shaped  sporocyst,  spread- 
ing out  at  one  end  to  form  an  attachment  disc  (Figs.  157,  158).  At  the  end 
opposite  the  attachment  organ  the  cercariae  develop  from  the  maturation 
of  the  germinal  epithehum.  They  escape  thru  a  rent  in  the  wall  of  the  sporo- 
cyst. Stages  in  development  (Fig.  158,  A-E)  are  similar  to  those  described 
for  C.  gracillima  (Fig.  143).  On  the  whole  the  embryos  of  this  species  are 
stouter  than  those  of  C.  gracillima. 

The  excretory  system  has  the  features  common  to  all  furcocercariae.  The 
bladder  and  the  eyelet  are  muscular  (Fig.  155).  The  lateral  tubes  are  of 
small  diameter,  with  anterior  and  posterior  tubules.    No  anastomoses  take 


83]  UFE  HISTORY  OF  TREMA  TODES—FA  UST  83 

place  in  the  cercariae  of  this  species.  The  median  tail  tube  receives  six  lateral 
tributaries,  the  anteriormost  of  which  is  reflexed.  The  rami  have  each 
an  unbranched  tubule. 

The  cephalic  region  is  marked  by  a  large  invertible  sucker,  extending 
thru  the  anterior  third  of  the  body.  No  intestinal  ceca  whatever  have  been 
observed  in  this  species.  No  glands  surround  the  esophagus  as  a  distinct 
ring,  altho  the  entire  esophageal  tube  lining  is  glandular  in  nature.  Four 
small  salivary-mucin  glands  are  situated  in  the  posterior  third  of  the  body 
(Fig.  155).  Their  thick  ducts  empty  into  the  oral  cavity  as  heavy 
bundles.  The  cells  of  this  system  are  filled  with  closely  aggregated,  deeply 
staining  granules.  The  nucleus  of  the  salivary-mucin  gland  cell  is  extremely 
small. 

This  species  possesses  neither  pigment  eye  nor  eye-spot  without  pigment. 

Encystment  has  not  been  observed  in  this  species. 

Cercaria  tuberistoma  is  probably  a  schistosomatid  larva. 


84  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [84 


PATHOLOGY 

The  infection  in  any  case  of  internal  parasitism  suggests  an  inquiry  as 
to  the  effects  of  the  parasite  on  the  host.  The  injury  on  the  human  sub- 
ject produced  by  trematode  infections  has  been  the  subject  of  numerous 
observations  and  records.  Notable  among  these  are  the  contributions  of 
Looss  (1913)  on  Schistosoma  haematobium,  Katsurada  (1914)  on  Schistosoma 
japonicum,  and  Ward  (1909)  on  Fasciolopsis  spp.  Again,  the  effect  of  tre- 
matodes  on  their  host  has  been  the  subject  of  considerable  study  in  fish  infec- 
tion, on  account  of  the  economic  importance  of  the  problem.  But  -where  the 
special  incentives  to  the  problem  have  been  lacking,  very  little  study  has  been 
made  on  the  pathological  significance  of  trematode  infection. 

The  helminth  parasite  causes  a  two-fold  injury  to  the  host,  mechanical 
and  chemical.  The  inclusion  of  parasites  within  the  organs  of  the  host  is  the 
occasion  for  distension  of  the  organs  and  consequent  irritation;  the  piercing 
of  organs  of  the  host  by  the  armature  of  the  worm,  an  actual  mechanical, 
injury.  These  injuries  are  accompanied  by  the  formation  of  fibromata  within 
the  organs  and,  usually,  attempts  to  isolate  the  parasite  by  the  secretion  of  a 
cyst  around  it,  as  in  schistosomiasis  (Bovaird  and  Cecil,  1914:191).  In  the 
ordinary  infection  a  toxin  is  secreted  by  the  parasite,  and  frequently  an  anti- 
thrombin  and  a  hemolysin  are  produced.  Such  injuries  as  these  in  higher 
animals  are  diagnosed  by  the  blood-picture,  where  excessive  hemocytolysis 
and  eosinophilia  are  found. 

The  infected  organs  of  the  molluscan  hosts  of  the  Bitter  Root  Valley  are 
the  liver  ceca.  Altho  these  Ue  next  to  the  testes,  the  worms  have  never  been 
found  to  invade  these  organs.  Thomas  (1883:114)  found  that  the  cercariae 
of  Fasciola  hepatica  live  normally  in  the  pulmonary  chamber  of  the  snail 
Lymnaea  trunculata.  Cort  (1915)  found  the  infected  organs  of  the  Campelomas 
were  the  gills,  but  in  other  species,  the  Hver  tissues  were  the  seat  of  the  infec- 
tion. The  infected  tissue  of  the  Venezuelan  snail,  Planorhis  guadelupensis, 
is  the  testicle  according  to  observations  made  by  the  writer. 

The  liver  ceca  consist  of  polygonal  lymphocytoidal  cells  grouped  around 
the  liunina  of  the  ceca,  with  an  epithelial  Uning  surrounding  the  ceca.  Among 
the  ceca  are  large  interstices  filled  with  lymph.  These  intercecal  spaces  are 
the  places  where  the  worms  are  first  found,  suggesting  invasion  thru  the  blood 
stream.  In  light  infections,  the  parthenitae  lie  here,  absorbing  the  nourish- 
ment from  the  surrounding  liquid  in  which  the  worm  is  bathed.  Ths  only 
mechanical  injury  up  to  the  time  of  the  activity  of  the  cercariae  is  caused  by 
the  agitation  of  the  developing  larvae  encysted  within  the  host.  But  in  the 
case  of  heavy  infection,  especially  where  the  larva  does  not  encyst  within  the 
host,  where  it  works  its  way  out  into  the  water,  even  a  few  worms  may  cause 
considerable  mechanical  harm  to  the  host. 

In  an  examination  of  living  material  and  sections  of  infected  moUusk  Uver 
tissue,  no  infection  was  found  to  be  so  light  that  the  host  was  unharmed.     In 


85]  LIFE  HISTORY  OF  TREMA  TODES—FA  UST  85 

the  Cercaria  hiflexa  infection  of  Physa  gyrina  (Fig.  159),  where  the  cyst  mem- 
brane is  moderately  heavy,  many  ceca  are  uninjured,  yet  some  betray  the 
marks  of  injury.  One  such  injury  is  shown  in  the  figure.  In  this  case  the 
cells  of  the  ceca  have  undergone  only  a  little  change.  A  comparison  of  this 
condition  with  that  of  C.  micropharynx  infection  in  Lymnaea  proxima  (Fig. 

160)  and  C.  gracillima  infection  in  Physa  gyrina  (Fig.  161),  shows  a  compara- 
tively small  injury  in  the  former  tissue  and  a  severe  injury  in  the  latter  tis- 
sues. Both  the  latter  cases  show  tissue  degeneration.  The  chemical  change 
in  Lymnaea  proxima  is  evinced  by  1)  fatty  bodies  that  have  accumulated  in 
some  of  the  cells  (a),  showing  as  highly  refractive  inter-cellular  inclusions; 
2)  large  vacuoles  in  the  cells  (6),  especially  around  the  nuclei;  3)  cytolysis  and 
karyolysis  (c,  d),  including  a  sloughing  of  the  tissues  in  the  region  of  the  lumina 
of  the  ceca.    The  condition  of  C.  gracillima  infection  in  Physa  gyrina  (Fig. 

161)  pictures  a  further  degeneration  of  the  tissues.  Fatty  globules  {b),  are 
common,  usually  accumulated  as  spherules  within  the  wall.  Vacuolization 
{d)  has  progressed  to  an  advanced  stage.  Cytolysis  and  karyolysis  (a,  c) 
have  gone  so  far  that  the  outlines  of  the  majority  of  the  cells  are  indistinct 
and  no  difference  exists  longer  between  the  epitheUal  and  the  lymphocytoidal 
cells.  An  indefinite,  irregular  margin  marks  off  the  ceca  from  the  interstices 
in  which  the  cercariae  lie.  A  further  change  consists  in  the  formation  of 
fibromata  {e)  and  granulomata  within  the  degenerating  ceca.  Finally  the 
epithehum  surrounding  the  entire  liver  mass  has  been  penetrated  by  sand 
granules  (/),  and  other  foreign  bodies  have  had  access  to  the  tissues. 

In  the  infection  of  Planorbis  irivolvis  with  C.  trisolenata  the  mass  of  the 
worms  was  about  twice  that  of  the  Uver  tissue  infected.  The  tissue  was  so 
distended  with  the  parasites  that  a  prick  of  the  needle  was  sufficient  to  cause 
the  liver  membrane  to  burst,  upon  which  the  rediae  and  cercariae  fairly  poured 
out  of  the  tissue. 

The  data  on  the  effect  of  the  trematode  infection  on  the  molluscan  host 
are  significant.  No  infection  is  so  light  that  mechanical  and  chemical  injuries 
are  not  inflicted.  In  the  heavy  infections  such  as  are  conmion  to  the  moUusks 
of  the  Bitter  Root  Valley,  the  injury  is  so  heavy  that  it  must  alter  appreciably 
the  Hfe  of  the  host.  The  mechanical  pressure  tends  to  inhibit  or  increase  the 
functioning  of  the  glandular  organs  and  cramps  the  tissues  within  unusual 
confines.  The  presence  of  foreign  proteins  in  close  association  with  the  lymph 
sinuses  is  sufficient  to  alter  the  vital  economy  of  the  host.  The  boring  of  the 
worm  destroys  the  tissues  locally  and  in  general  irritates  the  mechanism, 
exposing  it  to  bacterial  infection.  The  secretion  of  digestive  juices  by  the 
parasite,  and  of  anti-thrombins  and  possibly  specific  poisons,  upsets  the 
entire  physiological  equilibrium  of  the  organism. 


86  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [86 

PROBLEMS  PRESENTED 

INTERRELATION  OF  TREMATODES 

In  working  out  new  species  of  organisms,  especially  from  new  geographi- 
cal areas,  there  are  often  physiological  and  morphological  facts  that  are 
of  general  significance  in  the  light  of  previous  studies.  Relationship  is  the 
ultimate  problem  for  all  workers  in  morphology.  While  light  is  shed  on 
phylogeny  by  the  discovery  of  new  species,  it  is  futile  to  expect  to  found  a 
system  of  phylogeny  on  a  single  species.  With  these  limitations  in  mind  the 
writer  presents  some  of  the  more  important  questions  that  arise  from  the 
study  of  the  trematodes  of  the  mollusks  of  the  Bitter  Root  Valley. 

In  the  early  days  cercariae  and  rediae  were  considered  as  different  groups 
of  the  animal  kingdom,  and  it  was  not  until  the  life-history  studies  of  Leuckart, 
La  Valette  (1855),  and  Ercolani  (1881,  1882)  had  been  pubUshed  that  the 
genetic  relationships  of  cercariae  and  parthenitae  were  established.  The 
germ  layers  of  all  generations  of  trematodes  have  a  similar  origin,  and  impor- 
tant structures  of  the  group  present  the  same  problem. 

Certain  investigators  of  recent  time  have  come  to  regard  the  trematodes 
as  a  polyphyletic  group.  Their  conclusion  has  resulted,  perhaps,  from  their 
lack  of  study  and  consequent  inability  to  recognize  the  fimdamental  resem- 
blance of  the  genital,  excretory  and  nervous  systems  of  the  various  sub-divi- 
sions of  the  group,  especially  dming  the  developmental  stages. 

From  more  convincing  observations  Odhner  (1907)  has  concluded  that  the 
Monostomata  are  poU'phyletic.  He  has  noted  among  certain  monostomes  a 
structure  comparable  to  the  pharyngeal  pockets  of  amphistomes,  and  among 
others  a  primitive  acetabulum  (1911).  In  a  study  of  monostome  cercariae 
from  the  Bitter  Root  Valley,  the  similarity  of  the  nervous  system  and  genital 
cell  masses  of  Cercaria  peUucida  and  of  those  systems  in  Gastrothylax  gre- 
garius  Looss  has  been  investigated. 

Both  Cercaria  peUucida  and  Gastrothylax  gregarius  show  paired  brain 
ganglia  closely  set  together  with  only  slight  constriction  of  the  dorsal  com- 
missure. In  both  species  the  nerve  cells  lie  superficially  upon  the  central 
nerve  gangUon  masses.  IVIoreover,  relatively  large  posterior  ventral  and 
smaller  lateral  and  dorsal  tnmks,  together  with  their  respective  positions, 
constitute  a  series  of  similarities  not  to  be  overlooked.  The  lack  of  pharyn- 
gealis,  palatinus,  and  dorsolateral  commissure  (Figs.  123,  124)  serves  to 
show  that  the  nerve  complex  of  the  monostome  larva  Cercaria  pdlucida  is 
not  t>'pically  distomate.  Its  nerve  structures  are  much  more  readily  referred 
to  the  Gastrothylax  type. 

In  the  second  place  certain  features  of  the  genitalia  of  Cercaria  peUucida 
and  Gastrothylax  suggest  a  common  ancestry.  The  median  ovar>'  in  the 
subcaudal  region;  the  paired  testes  lateral  to  the  ovary;  the  dendritic  vitel- 
laria,  located  in  two  series,  and,  finally,  the  parallel  course  of  the  uterus  and 


87]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  87 

the  vas  efferens  to  the  genital  pore  far  cephalad — ^all  of  these  show  in  common 
a  genital  system  quite  distinct  from  the  usual  distome  types. 

The  similarity  of  the  nervous  and  genital  complexes  of  larval  monostomes, 
such  as  Cercaria  pellucida  and  C.  konadensis,  and  the  amphistome,  Gastro- 
thylax  gregarius,  suggest  a  common  origin  of  certain  monostomes  and  amphi- 
stomes. 

Among  adult  distomes  there  is  great  variety  of  structure,  yet  only  in  one 
family,  the  Schistosomatidae,  has  the  nervous  system  been  fundamentally 
altered.  The  structures  of  the  two  furcocercous  larvae,  Cercaria  gracilUma 
and  C.  tuberistoma,  demonstrate  their  relationship  to  the  Schistosomatidae. 
The  reasons  for  this  beUef  are  these: 

The  characters  which  distinguish  the  apharyngeal  furcocercous  cercariae 
are  as  follows:  1)  a  forked  tail  (larval  character  only);  2)  paired  groups  of 
salivary-mucin  glands  (larval);  3)  absence  of  an  oral  suctorial  disc,  and  in 
its  place  4)  an  invertible  suctorial  proboscis;  5)  an  apharyngeal  esophagus,  pro- 
vided with  glands  in  the  region  usually  occupied  by  a  pharynx.  The  nervous 
system,  more  deeply  seated,  is  modified  by  the  degeneration  of  the  posterior 
laterales  during  early  embryonic  development,  and  the  fusion  of  the  posterior 
dorsales  with  the  posterior  ventrales  about  one-third  the  body  length  back 
from  !the  anterior  end  (Fig.  150).  All  of  these,  except  the  forked  tail  and 
the  saUvary-mucin  glands,  are  both  larval  and  adult  characters.  In  addi- 
tion, the  larva  of  Cercaria  gracilUma  has  several  testicular  follicles  proliferated 
from  the  testes-mass  at  the  posterior  end  of  the  body. 

Certain  of  the  structures  of  this  group  also  characterize  the  larvae  of  other 
groups  of  trematodes.  For  example,  Cercaria  cristata  La  Val.  (1855:23;  Taf. 
II,  Fig.  K),  has  a  bifid  tail  and  apparently  lacks  a  pharynx,  but  the  fact  that 
it  lacks  an  acetabulum  probably  separates  it  from  the  distome  f urcocercariae. 
Among  the  Gorgorderinae  there  are  apharyngeal  cercariae  with  several  testes. 
However,  Ssinitzin  (1905:46-51;  Taf.  I,  II)  has  shown  for  four  Gorgordera 
species,  that  the  cercariae  are  characterized  in  common  by  1)  a  stylet,  2) 
salivary  glands  only  in  the  cephalic  region  of  the  body,  3)  a  large  glandular 
excretory  vesicle,  almost  filling  the  posterior  third  of  the  body,  and  4)  a  dis- 
proportionately large  tail,  showing  the  cystocercous  relation  of  the  larvae  of 
the  group.  Moreover,  the  nervous  system  of  the  Gorgorderinae  is  typically 
distomate  (Zailer  1914:386). 

It  may  be  stated  with  considerable  probabihty  that  all  of  the  fundamental 
organs  of  the  f urcocercariae,  namely,  the  apharyngeal  esophagus,  the  multiple 
testes,  and  the  uniquely  modified  nervous  system,  are  found  in  only  one 
family,  the  Schistosomatidae.  All  described  Schistosomatidae  are  charac- 
terized by  the  absence  of  a  true  oral  suctorial  disc  and  by  the  presence  of  an 
invertible  oral  suctorial  pouch.  They  have  no  pharynx,  but  in  its  stead 
glands  that  line  the  wall  of  the  esophagus.  Looss  has  described  the  modified 
nervous  system  of  the  family  in  his  study  of  Schistosoma  haematobium  (1895: 


88  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [88 

60-68;  Taf.  II,  Fig.  18).  It  corresponds  in  detail  to  the  system  in  Cercaria 
gracilUma  previously  described. 

Coupled  with  these  morphological  likenesses  are  the  experimental  data 
of  Leiper  (1915,  1916),  Miyuri  and  Suzuki  (1914),  and  Iturbe  and  Gonzalez 
(1917)  on  Schistosoma  life-histories.  Leiper  has  found  that  the  three 
schistosome  species  known  to  infect  man,  Schistosoma  haematobium,  S.  man- 
soni,  and  S.  japonicum,  give  rise  to  miracidia  which  have  a  certain  attraction 
for  certain  snails  in  the  districts  infected.  Within  the  tissues  of  these  snails 
the  miracidia  metamorphose  into  sporocysts,  and  the  second  generation  sporo- 
cysts  give  rise  internally  to  bifid  cercariae  with  a  ventral  sucker  but  without 
a  true  pharynx.  Furthermore,  these  cercariae  introduced  thru  the  skin  of 
experimental  animals,  mice  and  monkeys,  give  rise  to  typical  unisexual  adult 
schistosomes. 

This  two-fold  evidence  favors  the  view  that  the  furcocercous  apharyngeal 
distome  cercariae,  including  Cercaria  gracillima  and  C.  tuberistoma  of  the  Bitter 
Root  fauna,  develop,  under  proper  conditions,  into  adult  schistosomes.  One 
character  figured  by  Leiper  for  all  of  his  apharyngeal  bifid  cercariae,  yet  not 
used  by  him  as  a  diagnostic  character,  is  the  presence  of  saUvary-mucin  glands. 
On  the  other  hand,  one  character  used  by  Leiper  for  cercariae  of  the  group, 
namely,  the  absence  of  a  pigment  eye,  holds  for  his  three  species  of  schistosome 
larvae,  but  does  not  hold  for  Cercaria  ocellata  La  Val.,  C.  douthitti  Cort,  or  C. 
gracillima.  It  has  been  shown  that  the  eye-spot  may  be  present  without 
pigment  (C  gracillima).  Likewise  the  failure  of  Looss  to  mention  an  eye- 
spot  for  C.  vivax  Sons.  (1896:216-223;  Figs.  172-174)  does  not  necessarily 
imply  the  absence  of  pigmentless  eye-spots  in  that  species. 

The  relationship  of  the  forked  tail  apharyngeal  distome  cercariae  will 
be  made  much  clearer  by  a  consideration  of  the  genital  organs.  The  adult  Schis- 
tosomas into  which  the  larvae  of  Leiper  develop  are  characterized  by  a  relatively 
small  number  of  testicular  folUcles,  4  to  5  for  S.  haematobium,  6  to  8  for  .5. 
japonicum,  and  8  for  S.  mansoni.  On  the  other  hand,  the  testicle  prolifera- 
tion in  Cercaria  gracillima  (Fig.  149)  shows  twenty-four  or  twenty-five  fol- 
licles already  differentiated  from  a  posterior  germ  mass.  The  large  number 
of  testicular  follicles  has  been  found  to  be  characteristic  of  the  adult  Schisto- 
somatidae  of  the  genera  Bilharziella  (Kowalewski,1895;  1896),  Gigantobil- 
harzia  (Odhner,  1912),  and  Ornithobilharzia  (Odhner,  1912).  None  of  these 
genera  and  in  fact  no  Schistosomatidae  have  been  reported  from  North 
America. 

From  these  considerations  it  seems  probable  that  Cercaria  gracillima  is 
the  larva  of  a  schistosome  genus,  such  as  Bilharziella,  Ornithobilharzia  or 
Gigantobilharzia,  all  of  which  are  bird  parasites. 

Since  the  germinal  masses  of  Cercaria  gracillima  are  hermaphroditic,  and 
any  marked  differentiation  of  the  organs  does  not  take  place  while  the  larva 
is  outside  the  definitive  host,  differentiation  of  sex  in  Schistosomatidae  takes 
place  in  these  species  comparatively  late  in  their  metamorphosis.    This  view 


89]  LIFE  HISTORY  OF  TREMA  TODES—FA  UST  89 

is  in  keeping  with  the  studies  of  Odhner  (1912),  who  points  out  the  fundamen- 
tal morphological  relationship  of  the  hermaphroditic  species  Liolope  and 
Haplometra  to  the  unisexual  BUharziella,  Gigantobilharzia,  Omithobilharzia, 
and  Schistosoma. 

The  discussion  leads  to  the  conclusion  that  the  furcocercous  larvae  possess 
in  common  1)  a  bifid  tail,  2)  a  ventral  sucker,  3)  an  oral  suctorial  pouch  which 
can  be  inverted,  4)  a  glandular  esophagus  without  sphincter  muscles,  5) 
paired  groups  of  salivary-mucin  glands,  four  or  more  to  the  group,  6)  multiple 
testes,  and  7)  a  specifically  modified  nervous  system.  In  the  light  of  present 
knowledge  all  of  these  species  fall  within  the  limits  of  the  family  Schistoso- 
matidae. 

Of  all  the  known  groups  of  trematodes  the  Holostomata  have  been  the 
group  of  least  genetic  study  and  most  erroneous  interpretation.  On  account 
of  their  large  size  the  adult  holostomes  have  been  known  for  many  years  and 
dozens  of  species  have  been  described.  Nothing,  however,  has  been  known 
of  the  parthenitae  and  their  development.  Without  sufficient  evidence 
Brandes  (1891:573)  has  interpreted  the  sketch  of  a  miracidium  of  Strigea 
(Holostomum)  cornucopiae  Molin  (von  Linstow,1877,  Fig.30)  as  a  metamorphos- 
ing tetracotyle.  In  other  words,  Brandes  concludes  that  the  holostome  has 
a  direct  development  without  the  intercalation  of  a  parthenogenetic  cycle. 
Ercolani  (1881:284-290;  Tav.  II,  Figs.  16-22)  has  worked  out  the  life-history 
of  Strigea  erratica  (Duj.)  from  the  tetracotyle  to  the  adult  form,  by  infecting 
Anas  sp.  with  Tetracotyle  typica  cysts  from  the  mollusk  Planorhis  corneus. 
Altho  Ercolani  found  a  tetracotyle  in  a  sporocyst  (Tav.  II,  Fig.  18),  he  inter- 
preted it  as  the  invasion  of  the  tetracotyle  into  the  sporocyst  of  Cercaria 
ocellata  La.  Ya\.  Ssinitzin  (1910:22,  23)  has  justly  criticized  Brandes'  con- 
clusion of  the  monogenetic  development  of  holostomes,  but  in  lieu  of  true 
holostome  evidence  in  support  of  the  digenetic  view  he  has  substituted  evidence 
from  Cercaria  plicata,  a  peculiar  distome  larva  which  he  has  found  to  bear 
certain  relationships  to  the  holostomes. 

It  has  been  shown  in  this  paper  (p.  16)  that  there  are  parthenogenetic 
cycles  in  Cercaria  flabelliformis,  a  typical  holostome,  and  that  several  genera- 
tions of  rediae  are  intercalated  between  the  miracidium  and  the  tetracotyle. 
Thus,  there  is  conclusive  proof  that  the  holostome  has  an  alternation  of  genera- 
tions, hermaphroditic  and  parthenogenetic,  similar  in  kind  to  such  alternation 
in  other  Digenea. 

In  spite  of  the  strangely  modified  suctorial  apparatus  and  posterior  genital 
organs  of  the  holostomes,  there  seem  to  be  good  grounds  for  beUeving  that 
they  originated  from  the  distomes.  They  have  an  acetabulum,  and  frequently 
the  muscular  rudiment  of  a  genital  pore  just  in  front  of  the  acetabulum  (Fig. 
52).  On  the  other  hand  it  is  very  doubtful  if  the  lappets  (Zapfenlappen  of 
Brandes  1892,  Taf.  41,  Figs.  5-15)  bear  any  homology  to  the  genital  pore 
rudiment.  It  has  been  shown,  in  fact,  that  the  lateral  lappets  in  Cercaria 
flabelliformis  arise  from  a  pair  of  oval  suctorial  grooves  (Fig.  41),  and  that  in 


90  ILLINOIS  BIOLOGICAL  MONOGRAPHS  pO 

Tetracotyle  pipientis  (Fig.  47),  where  these  grooves  remain  rudimentary,  no 
I  ateral  lappets  develop. 

As  von  Linstow  (1877:189)  pointed  out,  species  characters  in  Strigea 
(Holostomum)  have  been  treated  very  superficially,  since  the  group  members 
are  not  readily  distinguished  by  external  markings  and  the  internal  anatomy 
is  difficult  to  interpret.  Yet  the  writer  has  found  that  even  in  the  early 
larva  the  points  of  differentiation  are  well  marked.  The  parthenogenetic 
egg  of  the  holostome  developing  into  the  cercaria  is  at  the  time  of  matura- 
tion structurally  different  from  the  ova  developing  into  a  redia.  Thus  the 
actual  phylogenetic  history  of  the  group  is  hidden  by  its  precocity  and  the 
developmental  stages  of  the  holostome  show  only  in  telescopic  fashion  the 
actual  ancestral  history. 

Extraordinary  nerve  modification  in  the  holostomes  (Fig.  53)  is  related 
directly  to  the  modification  of  the  muscle  complex.  This  modification  con- 
sists usually  in  the  degeneration  of  the  posterior  dorsales  and  laterales,  and 
a  relative  increase  in  size  and  importance  of  the  posterior  ventrales.  The 
other  systems  of  the  holostomes,  especially  the  genital  and  excretory  organs, 
are  equally  highly  modified  and  equally  well  formed  in  the  larva.  Ssinitzin 
(1910,  1911)  has  suggested  that  the  change  in  the  genital  pore  from  the  pre- 
acetabular  position  to  the  posterior  ventral  extremity  has  come  about  thru 
the  formation  of  a  new  opening  rather  than  thru  a  shifting  of  the  old  pre- 
acetabular  pore.  The  original  pore  is  still  present  in  the  larvae,  altho  in  most 
cases  there  is  no  clue  to  its  former  connection  or  function.  The  extent  of 
these  changes  indicates  a  long  period  of  gradual  adjustment  to  a  modifying 
environment. 

The  study  of  the  cercariae  of  the  various  groups  of  the  Digenea  not  only 
serves  to  supplement  relationship  studies  in  adult  hermaphroditic  generations 
of  trematodes,  but  also  brings  out  structural  relationships  very  considerably 
if  not  entirely  hidden  in  the  adult.  The  most  constant  of  all  the  systems  in 
the  group  Digenea  is  the  nervous  system.  Any  marked  modification  from 
the  characteristic  distomate  type  is  indicative  of  a  considerable  period  of 
divergent  growth. 

The  fundamental  systems  of  the  hermaphroditic  generation  of  the  tre- 
matode  are  deep  seated;  they  are  well  formed  in  the  cercaria,  and  little  signi- 
ficant differentiation  takes  place  during  metamorphosis. 

RELATION  OF  TREMATODES  TO  OTHER  GROUPS 

Among  the  early  systematists  Trematoda  were  classified  with  the  Hiru- 
dinea  because  of  the  common  superficial  resemblance  of  the  two  groups. 
Even  as  late  as  1871  Schmarda  separated  the  Trematoda  from  the  Turbellaria 
and  Cestoda,  and  placed  them  with  the  Hirudinea  in  the  Cotylidea.  Balfour 
(1881:316,  317)  considered  a  direct  relationship  of  all  Metazoa  above  Coel- 
enterata  entirely  unsatisfactory  and  conceived  the  idea  of  referring  them 
all  back  to  the  trochophore  larva  which  possessed  radial  symmetry.    In  his 


91]  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  91 

monograph  on  Amphistomum  subclavatum,  Looss  (1892:156,  157)  com- 
pared the  proHferation  of  the  germ-balls  from  the  body  wall  of  the  parthenita 
to  the  production  of  eggs  and  spermatozoa  in  the  marine  polychaetes,  and 
suggested  that  other  embryonic  structures  of  the  trematode  were  comparable 
to  annelid  structures,  so  that  they  might  be  considered  of  phylogenetic  value. 
Recently  Ssinitzin  (1911:86)  has  spoken  of  the  resemblance  of  the  Trematoda 
to  Arthropoda  and  Trochelminthes,  in  view  of  the  absence  of  any  ciliary  integ- 
ument, in  place  of  which,  he  says,  the  cuticula  and  the  external  skeleton 
develop. 

During  this  time  the  theory  of  the  common  descent  of  the  Trematoda, 
Cestoda  and  Turbellaria  has  been  gaining  ground,  not  because  they  are  all 
"flatworms, "  as  Ssinitzin  insists,  but  on  the  homologies  of  the  genital,  excretory 
and  nervous  systems.  The  observations  of  Leuckart  (1886:140),  Schulze 
(1853:178-195),  and  Schneider  (1864:590-597)  all  support  this  view,  while 
Leuckart  even  saw  the  analogy  between  the  gutless  sporocyst  and  the  Acoela. 
Lang  (1884:669)  showed  that  the  nervous  system  of  the  Trematoda  and 
Turbellaria  was  homologous. 

With  the  work  of  Haswell  on  Temnocephala  (1888)  the  close  affinities 
of  the  Trematoda  and  the  Turbellaria  became  evident.  In  this  group  the 
excretory  system,  the  three  anterior  and  posterior  nerve  trunks,  the  anterior 
mouth,  and  the  dorsal  pigment  eyes — all  these  bridged  the  way  for  the  ac- 
ceptance of  the  thesis  that  the  Trematoda  and  the  Turbellaria  have  a  common 
ancestry. 

The  study  of  the  parthenogenetic  generations  of  the  Digenea,  to  which 
this  paper  is  devoted,  stands  in  support  of  this  thesis  and  contributes  the 
following  facts  towards  its  further  acceptance. 

1.  The  body  cavity  of  the  hermaphroditic  generations  of  trematodes  and 
of  Turbellaria  is  filled  with  differentiated  mesenchyme  and  connective  tissue. 
In  the  parthenitae  the  parenchyma  is  confined  to  the  body  wall  because  it  is 
less  diJGferentiated. 

2.  Both  Trematoda  and  Turbellaria  are  typically  flat,  with  a  pronounced 
bilateral  symmetry.  The  cylindrical  appearance  of  the  parthenitae  is  a 
secondary  modification  due  to  parasitism. 

3.  The  epidermis  of  Trematoda  and  Turbellaria  consists  of  a  single  layer 
of  cells.  In  the  sporocyst  larva,  the  miracidium,  and  in  the  Turbellaria,  the 
epithelial  layer  is  ciliated.  In  the  rediae  and  in  the  cercariae  the  layer  is 
usually  sloughed  off  before  maturity  and  in  its  place  the  basement  membrane  of 
mesodermal  origin,  serves  as  the  integument. 

4.  The  nervous  system  of  the  Monogenea,  the  Digenea,  and  the  Turbellaria 
is  reducible  to  a  common  type.  Two  brain  gangha  with  a  transverse  commis- 
sure, three  anterior  pairs  of  nerve  trunks,  and  three  anterior  pairs  of  nerve 
trunks — these  are  common  to  all  three  groups.  Moreover,  the  pigment  eye- 
spots  of  the  Turbellaria,  Monogenea,  and  Digenea  are  not  only  homologous, 
but  practically  identical  in  detail  (Hesse  1897;  and  page  52  this  paper).     In 


92  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [92 

each  case  one  or  more  ganglion  cells  fill  the  optic  cup.  In  each  it  can  be 
traced  to  the  brain  center.  Parasitism  has  caused  the  pigment  eye  to  degen- 
erate in  most  adult  Digenea.  Even  in  the  cercariae  it  is  pigmented  only  in 
certain  species;  other  species  have  lost  all  traces  of  pigment,  but  the  optic 
nerve  is  still  present  and  can  be  traced  to  the  brain  center.  In  many  cases 
it  has  been  lost,  even  in  the  cercariae.  Eye-spots  are  common  in  miracidia, 
but  are  lost  on  metamorphosis  into  the  sporocyst.  There  are  no  records  of 
eyes  in  rediae. 

5.  The  digestive  tract  of  the  cercariae  and  the  adult  hermaphroditic  genera- 
tions of  trematodes  is  usually  triclad.  In  the  redia  the  gut  is  rhabdocoel; 
there  is  a  pharynx  and  saUvary  glands  have  been  described  (Ssinitzin,  1911, 
and  pp.  63,  this  paper).  In  the  miracidium,  there  is  an  indication  of  a 
rhabdocoel  gut  and  salivary  glands  (Looss,  1892;  Miyuri  and  Suzuki,  1914), 
altho  these  are  usually  lost  in  the  adult.  In  the  Turbellaria  the  gut  is  triclad, 
polyclad,  rhabdocoel  or  acoel.  The  pharynx  is  ordinarily  present  and  salivary 
glands  are  common. 

6.  The  excretory  system  in  the  two  groups  is  at  first  a  single  pair  of  pro- 
tonephridia.  This  condition  is  found  in  miracidia,  rediae,  cercariae  and  Tur- 
bellaria alike.  The  capillaries,  whether  in  the  larva  or  adult,  end  in  flame 
cells. 

7.  The  genital  system  was  one  of  the  first  in  which  investigators  recog- 
nized the  relationship  between  the  Trematoda  and  the  Turbellaria.  The 
hermaphroditic  condition  in  the  hermaphroditic  generation  of  the  Trematoda  is 
strikingly  similar  to  that  of  the  Turbellaria,  with  the  common  genital  atrium 
in  all  groups  except  Acoela.  Parthenogenesis  in  parthenitae  is  the  result 
of  the  great  change  in  environment  of  these  cycles. 

Thus  the  main  trend  of  investigation  has  come  to  support  the  common 
origin  of  the  Trematoda  and  the  Turbellaria. 

LIFE  CYCLE  OF  THE  DIGENETIC  TREMATODES 

The  life-history  of  the  trematode  of  the  order  Digenea  consists  not  in  an 
alternation  of  sexual  and  asexual  generations,  but  rather  of  successive  sexual 
generations  which  are  parthenogenetic  and  hermaphroditic. 

A  problem  which  has  arisen  in  connection  with  the  genitaUa  of  the  Digenea 
is  the  significance  of  Laurer's  canal.  Looss  (1893a)  considers  it  homologous 
to  the  uterus  of  Cestoda,  while  Goto  (1893)  beHeves  it  to  be  the  homolog  of 
the  blind  vagina  of  AmphiUna  and  the  genito-intestinal  canal  of  Monogenea. 
According  to  Liihe  (1909)  a  Laurer's  canal  is  present  in  Monostomes,  and  in 
some  groups  of  the  distomes,  including  Plagiorchiidae  and  Echinostomidae. 
It  has  not  been  recorded  for  holostomes  or  Schistosomatidae.  Except  for  the 
Echinostomid  cercariae,  a  Laurer's  canal  has  been  found  in  all  cercariae  of 
the  groups  studied  by  the  writer,  where  the  adult  trematode  has  the  canal. 
Absence  of  the  canal  in  Echinostomid  cercariae  can  be  explained  on  the 
basis  of  late  development  of  the  genital  organs  in  this  family.    On  the  other 


93 J  LIFE  HISTOR  Y  OF  TREMA  TODES—FA  UST  93 

hand,  no  Laurer's  canal  has  been  found  in  the  groups  where  no  canal  is  present 
in  the  adult.  Students  of  cercariae  have  not  as  a  rule  recorded  the  canal 
in  trematode  larvae.  Ssinitzin  (1905,  Figs.  62,  67,  74)  has  found  it  in  the  three 
xiphidiocercariae,  Cercaria  gibba  de  Fil.,  C.  prima,  and  C.  secunda.  The 
constant  development  of  this  organ  in  the  several  groups  described  in  this 
paper  shows  that  the  canal  originally  had  an  important  place  in  the  genital 
processes  of  the  Digenea. 

The  pronounced  difference  in  structure  between  parthenogenetic  ova  which 
develop  into  rediae  and  those  which  develop  into  cercariae  has  been  discussed 
(p.  18).  This  difference  has  been  found  to  bear  no  relation  to  the  phenomenon 
of  maturation,  since  the  chromosome  count  in  the  mature  cells  is  the  same, 
whether  redia  or  cercaria  is  to  be  produced.  In  fact,  it  seems  probable  that 
the  differentiation  occurs  before  maturation.  It  is  significant  that  the  ova 
which  develop  into  redia  are  comparatively  simple  while  the  ova  which  develop 
into  cercariae  are  extremely  complex.  In  this  connection  it  has  been  observed 
that  embryos  developing  from  germ-balls  produced  from  ova  free  in  the 
body  cavity  produce  daughter  rediae.  The  maturing  ova  from  the  germinal 
epithelium  lodged  in  the  body  wall  of  the  parthenita  develop  either  into  rediae 
or  cercariae. 

In  his  experiments  on  planarians  Child  (1915)  has  shown  that  starvation 
and  fragmentation  (fission)  secure  a  rejuvenescence  for  the  individual.  The 
less  differentiated  individual  is  on  the  whole  the  younger  one.  From  the 
present  study  on  the  life-history  of  trematodes  there  is  justification  for  the 
belief  that  the  undifferentiated  eggs  produce  daughter  parthenitae  because 
they  are  simple,  i.e.,  yoimger,  while  the  more  highly  differentiated  eggs  grow 
into  cercariae  because  they  are  physiologically  old.  Interpreted  in  this  light, 
the  parthenitic  individuals  of  the  Digenea  are  physiologically  younger  than  the 
cercariae  and  the  adult  hermaphroditic  forms  because  their  structure  is 
simpler.  They  have  sacrificed  complexity  of  structure  to  meet  the  needs  of 
the  parasitic  life,  and  in  so  doing  have  become  remarkably  rejuvenated.  In 
two  species,  Cercaria  diaphana  and  C.  micropharynx  extreme  simplicity  has 
been  assumed  in  the  sporocyst,  for  the  germ-balls  develop  from  any  cell  of 
the  body  wall. 

The  writer  believes  that  the  abihty  of  the  parthenita  to  reproduce  daughter 
rediae  or  sporocysts  for  two  or  more  generations  rests  on  the  simplicity  of  the 
ovum  and  the  relative  simplicity  of  the  parthenita,  especially  as  regards  the 
undifferentiated  mesoderm  cells.  If  this  rejuvenation  can  be  continued 
indefinitely,  the  parthenogenetic  generations  can  also  continue  indefinitely 
without  the  intercalation  of  the  hermaphroditic  cycle. 

Child  (1915:407)  has  stated  that  "in  many  cases  parthenogenetic  eggs 
are  apparently  less  highly  differentiated  morphologically,  and  younger  phy- 
siologically, than  zygogenic  eggs  of  the  same  species."  The  present  study 
makes  it  necessary  to  add  that  in  cases  where  the  parthenogenetic  eggs  may 
develop  into  parthenitae  or  cercariae,  the  eggs  which  develop  into  the  former 


94  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [94 

individuals  are  apparently  less  highly  differentiated  morphologically  and 
younger  physiologically  than  those  which  develop  into  cercariae. 

Finally  the  present  study  causes  the  writer  to  support  the  \'iew  that  the 
hermaphroditic  phase  of  the  life  cycle  of  the  Digenea  is  more  closely 
related  to  the  ancestral  group  than  the  parthenita,  and  that  the  simplicity  of 
the  parthenita  has  been  assumed  secondarily.  This  conclusion  is  based  on 
the  evidence  that  the  original  type  was  a  highly  complex  Platyhelminth  with 
ciliary  integimient  and  eye-spots,  characters  found  only  in  the  miracidium. 
The  modification  of  the  parthenita  has  come  about  as  the  direct  result  of 
parasitism.  It  has  lost  its  mesenchymatous  matrix,  its  excretory  tract  has 
been  extraordinarily  modified,  and  its  germ  cells  have  become  uniquely  sim- 
ple. The  nervous  system  of  the  redia  has  been  simplified  while  the  sporocySt 
lacks  a  nervous  system  entirely.  In  the  sporocyst  even  the  muscle  cells  have 
remained  undifferentiated.  Thus  complexity  in  the  hermaphroditic  genera- 
tion of  Digenea  is  an  index  of  the  unmodified  condition  of  the  group  most 
early    related    to    the    prototype. 

SUMMARY 

1.  Trematode  infection  of  mollusks  of  the  Bitter  Root  Valley,  Montana, 
is  heavy. 

2.  The  history  of  the  germ  cells  of  the  sporoc}'^st  and  redia  show  them  to 
arise  parthenogenetically. 

3.  Parthenitae  and  adult  hermaphoditic  trematodes  are  comparable  in- 
dividuals: likewise  their  germ  cells  can  be  referred  to  a  common  type  of  ger- 
minal epithehum. 

4.  The  integimient  of  trematodes  is  mesodermal  in  origin. 

5.  The  fundamental  systems  of  the  adult  hermaphroditic  trematode  are 
well  developed  in  the  cercaria. 

6.  The  excretory,  genital  and  nervous  systems  of  the  cercaria  may  be  used 
to  show  the  natural  relationships  of  the  larvae. 

7.  Holostomes,  like  dis tomes,  monostomes  and  amphis tomes,  have  an  al- 
ternation of  hermaphroditic  and  parthenogenetic  generations. 

8.  Holostomes  are  probably  of  distome  origin. 

9.  Parthenitae  are  well  adapted  to  their  parasitic  life  because  their  struc- 
ture is  simple,  in  consequence  of  which  they  have  become  physiologically 
young. 


95]  LIFE  HISTORY  OF  TREMATODES— FAUST  95 


SPECIES  DESCRIBED  IN  THIS  PAPER. 

MONOSTOMATA 

Cercaria  pellucida  Faust  1917 
Cer carta  konadensis  Faust  1917 

HOLOSTOMATA 

Cercaria  flabelliformis  Faust  1917 
Tetracotyle  pipientis  nov.  spec. 
Cercaria  ptychockeilus  Faust  1917 

DiSTOMATA 

Xiphidiocercariae 

Cercaria  crenata  Faust  1917 
Cercaria  glandulosa  Faust  1917 
Cercaria  diaphana  Faust  1917 
Cercaria  dendritica  Faust  1917 
Cercaria  micropharynx  Faust  1917 
Cercaria  racemosa  Faust  1917 

Echinostome  Cercariae 

Cercaria  trisolenata  Faust  1917 
Cercaria  biflexa  Faust  1917 

Furcocercariae 
Cercaria  gracillima  Faust  1917 
Cercaria  tuberistoma  Faust  1917 


96  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [96 


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1856.    De  la  Reproduction  chez  les  Trematodes  Endoparasites.    M6m.  de  I'lnst. 
Genevois,  3:1-280;  6  pi. 
NiTZSCH,   Ch.  L. 

1807.    Seltsame  Lebens-  und  Todesart  eines  bisher  unbekannten  Wasserthierchens, 
KiUan,  Georgia.  257-262;  281-286.    Cited  after  Braun  1893. 

1816.    Beitrag  zur  Infusorien-kunde  der  Naturbeschreibung  der  Zerkarien  und  Bazil- 
larien.    Neue  Schrift.  Nat.  Ges.  Halle  (1)  3;  1  Taf.    Reviewed  in  Isis,  1818:728 

NORDMANN,  A.  V. 

1832.    Mikrographische  BeitrSge.  I.    Berlin.  118  pp.,  10  Taf. 
Odhner,  T. 

1907.  Zur  Anatomie  der  Didymozoen:  ein  getrenntgeschlechtlicher  Trematode  mit 
rudimentaren  Hermaphroditismus.    Zool.  Studien  TuUberg,  1907:309-342;  1  Taf. 

1910.  Gigantobilharzia  acotylea,  n.g.,  n.sp.,  ein  mit  den  Bilharzien  verwandter  Blut- 
parasit  von  enormer  Lange.    Zool.  Anz.,  35:380-385;  5  Figs. 


100  ILLINOIS  BIOLOGICAL  MONOGRAPHS  IlOO 

1911.  Zum  natiirlichen  System  der  digenen  Trematoden.  1.    Zool.  Anz,,  37:181-191. 

1912.  Zum  natiirlichen  System  der  digenen  Trematoden.  V.    Zool.   Anz.,  41:54-71; 
7  Figs. 

Pagenstecher,  H.  a. 

1857.    Trematodenlarven  und  Trematoden.    Heidelb.  56  pp.,  6  Taf. 
Parona,  C,  e  Ariola,  V. 

1896.  Bilharzia  Kowalewskii  n.  sp.  nel  Larus  melanocephalus.  Boll.  Mus.  Zool.  e 
Anat.  Comp.  Univ.  Geneva,  45:1-3. 

POIRIER,   J. 

1886.    Tr6matodes  nouveaux  ou  peu  connus.    Bull.  Soc.  philomath.  Paris.    Seance  du 

28  Nov.  1885.    21  pp.  4  pi. 
Pratt,  H.  S. 

1909.    The  Cuticula  and  Subcuticula  of  the  Trematodes  and  Cestodes.    Amer.  Nat., 

43:705-729;  12  Figs. 
Rettger,  L.  J. 

1897.  Some  Additions  to  our  Knowledge  of  the  Anatomy  and  Embryology  of  the 
Holostomidae.    Proc.  Ind.  Acad.  Sci.,  1896:224,  225. 

Reuss,  H. 

1903.  Beobachtungen  an  der  Sporocyst  und  Cercaria  des  Distomum  duplicatum.  Zeit. 
wiss.  Zool.,  74:458-477;  1  Taf. 

ROSSBACH,    E. 

1906.  Beitrage  zur  Anatomie  und  Entwicklungsgeschichte  der  Redien.  Zeit.  wiss 
Zool.,  84:361-445;  4  Taf. 

ROSSETER,  T.   B. 

1909.  On  Holostomum  excisum  (Linstow,  1906)  and  the  Development  of  the  Tet- 
racotyliform  Larva  to  a  Holostomum  sp.  Jour.  Quek.  Micr.  Club,  (2)  10:385-392;  1  pi. 

RUDOLPHI,   C.  A. 

1819.    Entozoorum  SjTiopsis.    Berlin.    812  pp. 

SCHAUINSLAND,  H. 

1883.  Beitrage  zur  Kenntnis  der  Embryonalentwicklung  der  Trematoden.  Jenai. 
Zeit.  Naturwiss.,  16:465-527;  3  Taf. 

SCHMARDA,    L.    K. 

1871.    Zoologie.    Vol.  I.  Wien.    372  pp. 
Schneider,  A. 

1864.  Ueber  die  Muskeln  der  Wiirmer  und  ihre  Bedeutung  fiir  das  System.  Arch. 
Anat.  Physiol.,  1864:590-597. 

SCHULZE,  M. 

1853.    Zoologische  Skizzen.    Zeit.  wiss.  Zool.,  4:178-195. 

SCHWARZE,  W. 

1886.  Die  postembryonale  Entwicklung  der  Trematoden.  Zeit.  wiss.  Zool.,  43:41-86; 
1  Taf. 

SlEBOLD,  Th.  V. 

1835.    Helminthologische  Beitrage.  I.    Arch.  Naturgesch.,  (1)  1:45-83;  1  Taf. 
SsiNiTziN,  D.  Th. 

1905.  Distomes  des  poissons  et  des  grenouilles  des  environs  de  Varsovie.  Materiaux 
pour  I'histoire  naturelle  des  Trematodes  M6m.  soc.  nat.  Varsovie.  Biol.,  15:1-210,  6  pi. 
Russian. 

1910.  Studien  tiber  die  Phylogenie  der  Trematoden.    Biol.  Zeit.,  1:1-63;  2  Taf. 

1911.  La  generation  parthenogenetique  des  Trematodes  et  sa  descendance  dans  les 
mollusques  de  la  Mer  Noire.  Mem.  Acad.  Sci.  St.  Petersbourg,  (8)  30:1-127;  6  pi. 
Russian. 


101]  LIFE  HISTORY  OF  TREMATODES— FAUST  101 

Steenstrup,  J.  J.  S. 

1842.    Ueber  den  Generationswechsel  oder  die  Fortpflanzung  und  Entwicklung  dutch 

abwechselnde  Generationen.     Copenh.  60  pp. 
Stiles,  Ch.  W.,  and  Hassall,  A. 

1908.  Index  Catalog  of  Medical  and  Veterinary  Zoology.    Trematoda  and  Trematode 
Diseases.    U.  S.  Hyg.  Lab.  Bull.  37.    401  pp. 

Surface,  F.  M. 

1907.    The  Early  Development  of  the  Polyclad,  Planocera  inquilina.    Proc.  Acad.  Nat. 

Sci.  Phila.,  59:514-559;  6  pi. 
Tennent,  D.  H. 

1906.    A  Study  of  the  Life  History  of  Bucephalus  haimaenus:  a  Parasite  of  the  Oyster. 

Quart.  Jour.  Micr.  Sci.,  n.s.,  49:99-133;  2  pi. 
Thomas,  A.  P. 

1883.    Life  History  of  the  Liver  Fluke.    Quart.  Jour.  Micr.  Sci.,  23:99-133;  2  pi. 
Thoss,  E. 

1897.    Ueber  den  Bau  von  Holostomum  cucuUus  nov.  spec.    Leipzig.    66  pp.,  2  Taf. 
Ward,  H.  B. 

1909.  Fasciolopsis  buskii,  F.  Rathouisi,  and  Related  Species  in  China.    Trans.  Amer. 
Micr.  Soc,  29:5-16;  2  pi. 

1916.    Notes  on  Two  Free-Living  Larval  Trematodes  from  North  America.    Jour. 

Parasit.,  3:10-20;  1  pi. 
Wright,  S. 

1912.    Notes  on  the  Anatomy  of  Microphallus  opacus.    Trans.  Amer.  Micr.  Soc,  31: 

167-176;  2  pi.  , 

Zailer,  O. 

1914.    Zur  Kenntnis  der  Anatomic  der  Muskulatur  und  des  Nervensystem  der  Tre- 

matoden.    Zool.  Anz.,  44:385-396;  3  Figs. 


102 


ILLINOIS  BIOLOGICAL  MONGRAPHS 


[102 


EXPLANATION  OF  PLATES 
Abbreviations 


ad 

anterior  dorsalis  nerve 

ne 

nerrve  ending 

al 

anterior  lateralis  nerve 

np 

nervus  palatinus 

as 

anterior  sensory  field 

nph 

pharyngealis  nerve 

av 

anterior  ventralis  nerve 

ns 

subesophageal  commissure 

b,  be 

genital  atrium 

nt 

nerve  trunk 

bl 

bursa  glands 

o 

ovum 

br 

cerebral  ganglion 

od 

oviduct 

c,  ce 

cecum 

on 

oral  nerve  ring 

ca 

caudal  pocket 

op 

optic  nerve  cell 

ceg 

cercaria  germ-ball 

ope 

optic  cup 

eg 

caudal  gland  cells 

opn 

optic  nerve 

cr 

cirrus  pouch 

or 

oral  sucker 

cs 

collar  spines 

ot 

oot3^e 

d.dl 

salivary  gland  duct 

ov 

ovary 

dc 

dorsal  commissure 

P 

phar>-nx 

die 

dorsolateral  commissure 

pa 

parenchyma 

dp 

profundus  of  dorsalis  nerve 

pb 

polar  body 

ds 

superficialis  of  dorsalis  nerve 

pc 

preacetabular  commissure 

e 

epithelium 

pd 

posterior  dorsalis  nerve 

ee 

ectoderm 

pe 

preoral  sense  endings 

eg 

excretory  granules 

Pg 

primitive  genital  pore 

eb 

evertible  prepharynx 

Pgl 

locomotor  pocket  glands 

ep 

excretory  pore 

Pl 

posterior  lateralis  nerve 

es 

esophagus 

po 

postacetabular  commissure 

et 

excretory  tube 

pv 

posterior  ventralis  nerve 

ev 

excretory  vesicle 

pvc 

postero-ventrolateraJis  commissure 

ex 

excretory  tubule 

pvi 

postero-ventral  intermedius  nerve 

fe 

flame  cell 

r 

rhabdocoel  gut 

g 

genital  pore,  birth  pore 

rm 

ramus  muscularis  of  the  lateralis  nerve 

gb 

germ-ball 

rp 

ramus  palpalis  of  the  lateralis  nerve 

gle 

cystogenous  cell 

sg 

salivary  gland  cell 

i 

intermedius  nerve 

sp 

acetabular  spine 

igl 

digestive  gland 

st 

stylet 

1 

longitudinal  muscle  cell 

t 

basement  membrane 

Ic 

Laurer's  canal 

te,  t],2  testis 

le 

lateral  eye 

tr 

transverse  muscle  fiber 

Ig 

localized  germinal  epithelium 

u 

uterus 

Ip 

posterior  locomotor  pocket 

V 

vagina 

k 

lateral  suctorial  groove 

vd 

vas  deferens 

m 

myoblast 

ve 

vas  ef ferens 

me 

median  eye-spot 

vf 

vitelline  follicles 

mp 

musculus  preoralis 

vi 

vitelline  duct 

n.ne 

nerve  cell 

vs 

acetabulum 

The  lines  in  figures  6,  26,  51, 146, 147  have  a  value  of  0.5mm;  in  figures  5,  7, 13-17,  19-20, 
27-29,  31-34,  36,  37,  44-46,54,  56,  57,  61,  68-75,  77,  82,  83,  89,  91,92,97-99, 101, 102, 104, 107, 
108,  111-113,  118,  119,  121-133,  136,  138,  140,  141,  145,  150-154,  a  value  of  0.01  mm;  in  all 
other  figures,  a  value  of  0.05  mm. 


103]  UFE  HISTORY  OF  TREMATODES— FAUST  103 


PLATE  I 


104  ILUNOIS  BIOLOGICAL  MONOGRAPHS  (104 


DESCRIPTION  OF  PLATE 

Figs.  1-3. — Cercaria  pellucida;  sketches  of  progressive  stages  of  pigmentation;  dorsal  view, 

showing  two  lateral  eye-sp>ots  and  one  median  spot.  X  100. 
Fig.  4. — Cercaria  pdlucida;  dorsal  view,  somewhat  contracted.  X  100. 
Fig.  5. — Cercaria  pdlucida;  anterior  tip,  figuring  details  of  pigmentation  and  contents  of  the 

excretory  tube.  X  330. 
Fig.  6. — Cercaria  pellucida;  redia,^characteriz€d  by  extensive  rhabdocoel  gut  and  spinous 

prepharynx.  X  34. 
Fig.  7. — Cercaria  pellucida;  detail  of  the  spinous  prephar^Tix  of  the  redia.  X  540. 
Fig.  8. — Cercaria  pdlucida;  young  redia;  precocious  development  of  the  cercariae  before  the 

redia  is  mature.  X  38. 
Figs.  9-11. — Cercaria  pellucida;  three  stages  in  encystment.  X  38. 
Fig.  12. — Young  Cercaria  pdlucida;  origin  of  posterior  locomotor  pockets  within  the  caudal 

pocket.  X  170. 
Fig.  13. — Cercaria  pellucida;  transverse  section  thru  the  middle  of  the  body.  X  330. 
Fig.  14. — Cercaria  pdlucida;  detail  of  cystogenous  gland  cells  in  the  region  of  the  lateral  eye- 

spot.  X  330. 
Fig.  15.— Cercaria  pdlucida;  contracted  excretory  bladder  and  posterior  locomotor  pockets. 

X  238. 
Figs.  16,  17. — Cercaria  pellucida;  details  of  the  posterior  locomotor  pocket;  Fig.  16,  con- 
tracted; Fig.  17,  relaxed;  xx,  retractor  muscles;  yy,  reflexor  muscles.  X  540. 
Fig.  18. — The  genitalia  of  Cercaria  pdlucida;  r^ons  of  ootype  and  metraterm.  X  238. 
Fig.  19. — Cercaria  pellucida;  transverse  section  thru  tail,  indicating  arrangement  of  ordinary 

parenchyma  cells.  X  540. 
Fig.  19a. — Cercaria  pdlucida;  oblique  section  thru  tail,  indicating  arrangement  of  muscle 

fibers.  X  540. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


19  a 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  I 


1051  UFE  HISTORY  OF  TREMATODES— FAUST  105 


PLATE  II 


105  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [106 


DESCRIPTION  OF  PLATE 

Fig.  20. — Cercaria  pellucida;  sagittal  section  thru  pharynx  and  gut  of  redia,  with  prepharynx 

organ  retracted.  X  330. 
Fig.  21. — Cercaria  pellucida;  transverse  section  thru  body  in  region  of  posterior  locomotor 

pocket  glands.  X  170. 
Fig.  22. — Cercaria  pellucida;  optical  view  of  the  proliferation  of  the  germ-balls  from  the 

posterior  germinal  epithelium  of  the  redia.  X  330. 
Fig.  23. — Cercaria  pellucida;  central  nervous  system,  typical  for  the  trioculate  species  of 

monostome  cercariae.  X  330. 
Fig.  24. — ^Yoimg  Cercaria  pellucida;  oblique  section  thru  ganglion  mass,  sho';nng  connection 

of  eye-spots  with  brain  center.  X  330. 
Fig.  25. — Cercaria  konadensis;  dorsal  view.  X  105. 
Fig.  26. — Redia  of  Cercaria  konadensis.  X  34. 

Fig.  27. — Cercaria  konadensis;  detail  of  paired  group  of  caudal  gland  cells.  X  540. 
Fig.  28. — Cercaria  konadensis;  genital  cell  masses  in  region  of  ootype.  X  540. 
Fig.  29. — Cercaria  konadensis;  detail  of  excretory  bladder  and  posterior  locomotor  pockets. 

X  238. 
Fig.  30. — Cercaria  konadensis;  optical  view  of  the  germinal  rachis  of  the  redia.  X  330. 
Fig.  31. — Cercaria  konadensis;  sagittal  section  thru  aspinose  prepharynx  of  the  redia.  X  330. 
Fig.  32. — Mature  Cercaria  urbanensis  Cort;  transverse  section  thru  tail,  showing  caudal  gland 

cells.  X  330. 
Figs.  33, 34. — Cercaria  urbanensis;  stages  in  differentiation  of  caudal  gland  cells  from  ordinary 

parenchyma  cells.  X  330. 
Fig.  35. — Cercaria  urbanensis;  detail  of  excretor>'  vesicle  and  posterior  locomotor  pockets. 

X  238. 
Fig.  36. — Early  germ-balls  of  Cercar /a  «rJa»e«5J5;  oblique  section  thru  brain  mass  and  lateral 

eye-spot,  showing  ectodermal  origin  of  pigment  cup,  and  connection   with  optic  cells 

of  brain.  X  730. 
Fig.  37. — Oblique  longitudinal  section  thru   Cercaria  pellucida,  showing  detail  of  nerve 

endings.  X  730. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  II 


[107  LIFE  HISTORY  OF  TREMATODES— FAUST  107 


PLATE  III 


108  ILUNOIS  BIOLOGICAL  MONOGRAPHS  [108 


DESCRIPTION  OF  PLATE 

Fig.  38. — Cercaria  fldbdliformis;  ventral  view  of  worm  freed  from  cyst;  U,  lateral  lappets 

X  80. 
Fig.  39. — Cercaria  flabelliformis;  dorsal  view,  giving  details  of  the  excretory  system  and 

genitalia.  X  80. 
Fig.  40. — Cercaria  flabelliformis;  lateral  view,  showing  suctorial  cup  in  anterior  portion  of 

worm;  U,  lateral  lappets.  X  80. 
Fig.  41. — Immature  Cercaria  flabelliformis  within  cj'st.  X  54. 
Fig.  42. — Cercaria  flabelliformis;  yoimg  redia,  detailing  the  excretory  chaimels  in  the  worm. 

X  54. 
Fig.  43. — Cercaria  flabelliformis;  redia  showing  paired  salivary  glands  emptying  into  the 

oral  pocket.  X  54. 
Fig.  44. — Cercaria  flabelliformis;  mid-frontal  section  thru  young  daughter  redia  in  region  of 

germinal  cell  maturation.  X  330. 
Fig.  45. — Cercaria  flabelliformis;  median  frontal  section  thru  yoimg  daughter  redia,  showing 

proliferation  of  germinal  epithelium  at  posterior  end  of  gut.  X  330. 
Fig.  46  a-m. — Cercaria  flabelliformis  rediae;  matiu-ation  of  parthenogenetic  ova;  A,  resting 

cell;  B,  C,  formation  of  spireme;  D,  division  of  spireme  skein  into  eight  chromosomes;  E. 

P,  G,  longitudinal  splitting  of  chromosomes  at  equatorial  plate;  H,  mitosis,  with  forma. 

tion  of  polar  body  and  preparation  of  ovum  for  second  mitosis;    /,  polar  body  almost 

constricted  off,  chromosome  b  excentric;  /,  ovum  preparing  for  second  division,  polar 

body  also  dividing;  K,  cell  cleavage,  with  precocious  chromosomes  bi,  b2  excentric; 

L,  first  cleavage  of  a  cercaria-ov\mi,  with  polar  body  degenerating;  M,  metaphase  of  a 

somatic  cell  in  process  of  division.  X  1620. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUMES 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


1091  LIFE  HISTORY  OF  T REM ATODES— FAUST  109 


PLATE  IV 


no  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [110 


DESCRIPTION  OF  PLATE 

Fig.  47. — Tetracotyle  pipientis;  ventral  view,  showing  digestive  tract  and  genital  system. 

X  105. 
Fig.  48. — Tetracotyle  pipientis;  diagram  of  the  excretory  system,  with  excretory  granular 

inclusions.  X  105. 
Fig.  49. — Cercaria  ptychocheilus;  ventral  view,  including  digestive,  excretory  and  genital 

systems.  X  105. 
Fig.  50. — Cercaria  ptychocheilus;  sketch  of  encysted  worm.  X  25. 

Fig.  51. — Cercaria  ptychocheilus;  sketch  of  ruptured  cyst  with  attachment  annulus.  X  25. 
Fig.  52. — Cercaria  ptychocheilus;  detail  of  genital  system.  X  165. 
Fig.  53. — Cercaria  ptychocheilus;  nervous  system.  X  330. 

Fig.  54. — Cercaria  ptychocheilus;  transverse  section  thru  middle  of  body.  X  540. 
Fig.  55. — Cercaria  crenata;  dorsal  view.  X  170. 

Figs.  56,  57. — Cercaria  crenata;  ventral  and  lateral  views  of  stylet.  X  540. 
Fig.  58. — Cercaria  crenata;  sporocyst.  X  54. 
Fig.  59. — Cercaria  crenata;  detail  of  genitalia.  X   170. 
Fig.  60. — Cercaria  glandulosa;  ventral  view.  X  370. 
Fig.  61. — Cercaria  glandulosa;  ventral  view  of  stylet.  X  370. 
Fig.  62. — Cercaria  glandulosa;  salivary  and  cystogenous  glands.  X  75. 
Fig.  63. — Cercaria  glandulosa;  detail  of  caudal  pockets,  showing  insertion  of  tail,  spinose 

lateral  grooves,  and  three-spined  ventral  flap.  X  100. 
Figs.  64,  65. — Cercaria  glandtilosa;  outline  of  excretory  vesicle,  open  and  closed.  X  200. 
Fig.  66. — Cercaria  glandulosa;  genital  cell  masses,  dorsal  view.  X  110. 
Fig.  67. — Cercaria  glandulosa;  sporocyst.  X  170. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  IV 


Ill]  UFE  HISTORY  OF  TREMATODES— FAUST  111 


PLATE  V 


112  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [112 


DESCRIPTION  OF  PLATE 

Figs.  68-70. — Cercaria  glandnlosa;  consecutive  frontal  sections,  giving  details  of  the  nervous 
system  anterior  to  the  brain.  X  540. 

Fig.  71. — Cercaria  glandtdosa;  frontal  section,  with  details  of  innervation  of  acetabulum. 
X540. 

Fig.  72-75. — Cercaria  glandulosa;  transverse  sections  thru  levels  aa  to  dd  oi  Fig.  60.  X  540. 

Fig.  76. — Cercaria  diaphana;  ventral  view,  considerably  flattened  by  cover  slip.  X  170. 

Fig.  77. — Cercaria  diaphana;  ventral  view  of  stylet.  X  540. 

Fig.  78. — Cercaria  diaphana;  ventral  view,  giving  details  of  glands  and  genital  cell  masses. 
X  170. 

Figs.  79,  80. — Cercaria  diaphana;  sporocysts.  X  80. 

Fig.  81. — Cercaria  dendritica;  ventral  view.  X  170. 

Figs.  82,  83. — Cercaria  dendritica;  lateral  and  ventral  views  of  stylet.  X  250. 

Fig.  84. — Cercaria  dendritica;  encysted  worm.  X  150. 

Fig.  85. — Cercaria  dendritica;  salivary  and  cystogenous  glands.  X  170. 

Fig.  86. — Cercaria  dendritica;  genital  system.  X  150. 

Fig.  87. — Cercaria  dendritica;  yoimg  sporocyst.  X  150. 

Fig.  88. — Cercaria  dendritica;  mature  sporocyst.   X  150. 

Fig.  89. — Cercaria  dendritica;  posterior  end  of  mature  sporocyst,  showing  origin  of  germ- 
balls  from  localized  germinal  epithelium.  X  330. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  V 


113]  LIFE  HISTORY  OF  TREMATODES— FAUST  113 


PLATE  VI 


114  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [114 


DESCRIPTION  OF  PLATE 

Fig.  90. — Cercaria  micro  pharynx;  ventral  view.  X  170. 

Figs.  91,  92. — Cercaria  micropharynx;  ventral  and  lateral  views  of  stylet.  X  540. 

Fig.  93. — Cercaria  micropharynx;  distribution  of  glands.  X  170. 

Fig.  94. — Cercaria  micropharynx;  sporocyst  with  non-localized  germinal  epithelium.  X 

Fig.  95. — Cercaria  micropharynx;  cercariae  encysted  in  old  sporocyst.  X  54. 

Fig.  96. — Cercaria  micropharynx;  genital  cell  masses.  X  170. 

Fig.  97. — Cercaria  micropharynx;  transverse  section  thru  brain  center.  X  540. 

Fig.  98. — Cercaria  micropharynx;  transverse  section  thru  excretory  comua.  X  540. 

Fig.  99. — Cercaria  micropharynx;  transverse  section  thru  tail.  X  540. 

Fig.  100. — Cercaria  racemosa;  ventral  view.  X  150. 

Figs.  101,  102. — Cercaria  racemosa;  ventral  and  lateral  views  of  stylet.  X  330. 

Fig.  103. — Cercaria  racemosa;  detail  of  salivary  glands.  X   150. 

Fig.  104. — Cercaria  racemosa;  genital  cell  masses.  X  330. 

Figs.  105,  106. — Cercaria  racemosa;  sporocysts,  showing  localized  germinal  epithelium  and 

attachment  organ,  ao.  X  54. 
Fig.  107. — Cercaria  racemosa;  lateral  view  of  genital  cell  masses  in  region  of  acetabulum. 

X  330. 
Fig.  108. — Cercaria  racemosa;  optical  view  of  the  sporocyst  in  region  of  birth-pore,  bp;  arrow 

points  toward  attachment  organ.  X  330. 
Fig.  109. — Cercaria  trisolenata;  ventral  view.  X  150. 
Fig.  110. — Cercaria  trisolenata;  dorsal  view  of  collar  spines.  X  170. 
Fig.  111. — Cercaria  trisolenata;  lateral  view  of  collar  spines.  X  330. 
Fig.  112. — Cercaria  trisolenata;  sketch  of  acetabular  spines.  X  540. 
Fig.  113. — Cercaria  trisolenata;  typical  cystogenous  cell  glands,  showing  granules  and  chro- 

midia.  X  540. 
Fig.  114.4-E. — Cercaria  trisolenata;  sketches  of  developmental  stages.  X  80. 
Fig.  115  A-C. — Cercaria  trisolenata;  stages  in  encystment.  X  80. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 

-st 


VOLUME  4 


LIFE  HISTORY  OF  TREMATODES 


PLATE  VI 


1151  LIFE  HISTORY  OF  TREMATODES— FAUST  115 


PLATE  VII 


116  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [116 


DESCRIPTION  OF  PLATE 

Fig.  116. — Cercaria  trisolenata;  encysted  worm.  X  150. 

Fig.  117. — Cercaria  trisolenata;  redia.  X  50. 

Fig.  118. — Cercaria  trisolenata;  longitudinal  and  transverse  muscle  fibers  of  the  digestive 
tract,  showing  myoblast  connections.  X  730. 

Fig.  119. — Cercaria  trisolenata;  peripheral  muscle  fibers  of  longitudinal  system.  X  730. 

Fig.  120. — Cercaria  trisolenata;  genital  cell  masses.  X  220. 

Fig.  121. — Cercaria  trisoleruUa;  butterfly  stage  in  development  of  the  central  nervous  system. 
X   330. 

Fig.  122. — Cercaria  trisolenata;  differentiating  stage  in  development  of  central  nervous  system. 
X  330. 

Figs.  123,  124. — Cercaria  trisolenata;  lateral  and  dorsal  views  of  central  nervous  system  of 
mature  cercaria.  X   330. 

Fig.  125. — Cercaria  trisolenata;  central  nervous  system  of  the  redia.  X  220. 

Fig.  126. — Cercaria  trisolenata;  distribution  of  nerve  cells  in  the  redia,  median  sagittal  sec- 
tion. X  330. 

Fig.  127. — Cercaria  trisdenata;  detail  of  the  peripheral  nerves  of  the  redia.  X  540. 

Figs.  128-133. — Cercaria  trisolenata;  traiisveTst  sections  at  levels  aatofol  Fig.  109.  X  330. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


LIFE  HISTORY  OF  TREMATODES 


PLATE  VII 


117]  UFE  HISTORY  OF  TREMATODES— FAUST  117 


PLATE  VIII 


118  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [118 


DESCRIPTION  OF  PLATE 

Fig.  134. — Cercaria  biflexa;  ventral  view,  showing  salivary  gland  cells.  X  105. 

Fig.  135. — Cercaria  biflexa:  ventral  view,  showing  excretory  system.  X  105. 

Fig.  136. — Cercaria  biflexa;  lateral  view  of  collar  spines.  X  330. 

Fig.  137. — Cercaria  biflexa;  redia  of  worm.  X  170. 

Fig.  138. — Cercaria  biflexa;  detail  of  three  flame  cells  in  cephalic  region.  X  540. 

Fig.  139. — Cercaria  biflexa;  genital  cell  masses.  X  170. 

Fig.  140. — Cercaria  trisolenata;  posterior  end  of  redia.  X  540. 

Fig,  141. — Cercaria  biflexa;  posterior  end  of  redia.  X  540. 

Fig.  142. — Cercaria  gracillima;  ventral  view.  X  230. 

Fig.  143.— Cercaria  gracillima;  excretory  system.  X  350. 

Fig.  144. — Cercaria  gracillima;  dorsal  view  of  trunk,  showing  eye-spots  and  salivary  glands 

X   350. 
Fig.  145. — Cercaria  gracillima;  detail  of  flame  cell  of  excretory  system.  X  750. 
Figs.  146,  147. — Cercaria  gracillima;  sporocysts;  Fig.  146,  x  14;  Fig.  147,  X  21. 
Fig.  148  A-G. — Cercaria  gracillima;  stages  in  development.  X  SO. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  VIII 


119]  UFE  HISTORY  OF  TREMATODES— FAUST  119 


PLATE  IX 


120  ILLINOIS  BIOLOGICAL  MONOGRAPHS  [120 


DESCRIPTION  OF  PLATE 

Fig.  149. — Cercaria  graciUima;  genital  cell  masses.  X  270. 

Fig.  150. — Cercaria  graciUima;  nervoiis  system.  X  540. 

Fig.  151. — Cercaria  graciUima;  central  nervous  system  in  a  very  yoimg  germ-ball.  X  540. 

Fig.  152. — Cercaria  graciUima;  transverse  section  thru  esophagus  glands.  X  540. 

Fig.  153. — Cercaria  graciUima;  transverse  section  thru  region  slightly  posterior  to  that  shown 

in  Fig.  152.  X  540. 
Fig.  154. — Cercaria  graciUima;  transverse  section  thru  salivary  glands.  X  540. 
Fig.  155. — Cercaria  tuberisloma;  ventral  view.  X  170. 
Fig.  156  A-F. — Cercaria  tuberisloma;  stages  in  development.  X  75. 
Figs.  157,  158. — Cercaria  tuberisloma;  sporocysts.  X  54. 
Fig.  159. — Cercaria  biflexa;  section  thru  liver  tissue  of  Physa  gyrina  Say,  showing  infection; 

a,  disintegrating  cecvmi;  b,  broken  down  connective  tissue;  c,  section  of  worm.  X  170. 
Fig.  160. — Cercaria  micropharynx;  section  thru  liver  tissue  of  Lymnaea  proxima  Lea,  infected 

with  the  worm;  a,  fatty  bodies  in  degenerating  cecimi;  b,  vacuoles;  c,  sloughing  tissue; 

d,  karyolysis;  e,  section  of  worm.  X  170. 
Fig.  161. — Cercaria  graciUima;  section  thru  liver  tissue  of  Physa  gyrina  Say  infected  with 

the  worm;  a,  cytolysis;  b,  fatty  globules;  c,  karyolysis;  d,  vacuoles;  e,  fibromata;/,  sand 

inclusions;  g,  section  of  worm.  X  240. 


ILLINOIS  BIOLOGICAL  MONOGRAPHS 


VOLUME  4 


FAUST 


LIFE  HISTORY  OF  TREMATODES 


PLATE  IX 


i 


